Free guide · 1995–2001 · M104, M119, M120
Mercedes SL R129: what to check before you buy
What this car is, and the six questions that decide whether the one you are looking at is a good buy.
In this guide · 6 chapters
Who built it, and what they built
A two-seat roadster with an electro-hydraulic soft top that stows itself under a rigid cover at the touch of a button — and a removable aluminium hardtop for the winter. Built for twelve years without the shape ever looking dated. In the years this guide covers — 1995 to 2001 — you could have it as the SL 320 with a 3.2 six, the SL 500 with a 5.0 V8, or the SL 600 with a 6.0 V12. Until spring 1998 the six is a straight six; after that the SL 320 has a V6 and the SL 500 a new V8. There was also an SL 280, and a series of AMG versions, which this guide does not cover separately.
What is unusual about it, specifically
It was engineered past the point where anyone was counting. A roof that folds itself away under a powered cover. A roll bar that rises out of the bodywork on its own when the car senses trouble. And, at the top of the range, twelve cylinders in a two-seater.
And it stayed in production for twelve years, which means late cars had a decade of fixes behind them while still being the same car underneath.
One piece of genuinely good news, and it is specific to these years
The wiring harness that everybody warns you about is less of a problem the later the car.
The R129 is famous for an engine loom whose insulation crumbles, causing misfires, sensor faults and electrical problems that nobody can reproduce. It sits mainly in the earlier cars, and the later cars in this guide are largely past it.
That does not make a late R129 immune, and you should still look. But if you have read a forum thread that made you afraid of this car, check which years it was about.
And one warning that shapes this whole guide
The expensive corrosion on this car is corrosion you cannot see. The sills and the tubular jacking points sit under plastic covers, and they rot underneath them for years while the paint above stays perfect. It is the one item on this list that can turn structural, and it is free to check.
How the figures in this guide work
There are no prices in here, and that is deliberate. A workshop rate differs by a factor of two or three between countries, so a figure we cannot verify for you is worse than no figure. What does not move is how much work a job is — that follows from what has to come off the car.
So every item says whether it is an hour or two, half a day, a day, two or three days, or a week or more in the workshop, and whether the money sits in the part or in reaching it.
The six questions that decide whether this car is a good buy
1 · What year is it, exactly?
1995 and later is what this guide is about. The later the car, the further it is from the wiring-harness years.
2 · May I take the sill covers off?
Ask before you travel. A seller who says yes has probably already looked. A seller who hesitates has told you something.
3 · Does the roof open and close fully, more than once, while I watch?
Eleven to twelve hydraulic units have to agree. One cycle proves less than you think.
4 · Is there any staining in the headlining near the header rail?
That is a known leak point for the roof hydraulics, and looking costs you nothing while the repair does not.
5 · Has the engine loom ever been replaced, and is there an invoice?
On a later car this is a bonus rather than a requirement — but if it has been done, it is done.
6 · Is there any wetness around the gearbox electrical connector?
On the five-speed automatic, fluid can escape there, travel along the harness and damage the transmission control unit. Worth one look.
Which years, which specification
Before mid-1993 it is a different car on paper. The R129 was sold as 300 SL, 300 SL-24, 500 SL and 600 SL until the summer of 1993, and as SL 280, SL 320, SL 500 and SL 600 afterwards. The badge tells you which side of that line a car is on, and it is more reliable than an advert.
This guide covers 1995 to 2001. That is the second half of the model's life: towards the end of the wiring problem, and with years of running changes behind it.
Which engine. The SL 320 is the one to own if you want to use it: six cylinders, and the simplest of the three. The SL 500 V8 is the one most people picture. The SL 600 V12 is magnificent and every job on it costs more, because everything has to come out to reach anything.
The engine change in 1998. In spring 1998 Mercedes replaced the engines of the SL 280, SL 320 and SL 500 with a new generation of V6 and V8 — the M112 and the M113 — with three valves and two spark plugs per cylinder. The SL 600 kept its V12. Check the engine on the individual car rather than the year on the advert.
What it is worth
Not in money, but in the only currency that matters when you are standing next to one.
An R129 is priced as an old Mercedes and repaired as a complicated one. Two systems can cost more than the car is advertised for: the roof, and structural corrosion in the sills.
So the value of a specific car is:
- what is under the sill covers, and
- what the roof does when you cycle it more than once, and
- whether the folder has a loom, a roof service, or neither.
A car with dry, sound sills and a roof that cycles without hesitation is worth substantially more than its advert suggests. A cheaper one with neither is the same car with the bills still in front of it.
What it is actually like to own one
Solid in a way that modern convertibles are not.
The R129 does not feel like a car with its roof cut off, because it was not engineered like one. It is heavy, quiet and extremely stable, and with the hardtop on in winter it is simply a coupe. The straight six of the earlier cars is smooth and unstressed; the V8 makes it effortless.
What it asks in return is that you use it and keep it dry. Hydraulics that never move seize. Drains that fill with leaves put water where the electrics are. The cars that go wrong are almost always the cars that stood.
The honest summary: a used R129 is an over-engineered Mercedes you can still buy cheaply, and the cheap ones are cheap for reasons that are visible if you look under the plastic.
The buying guide — €24
Everything above is what the car is. This is what you check.
Six faults that belong to this car, taken apart one by one, with how much work each repair is and how to tell which of them you are looking at. Twelve things that are simply thirty years old, every one with how much work it is, what tells you about it at a viewing, and whether it has to be done now, within a year or two, or not at all. Where an R129 shell rots out of sight, and what the plastic covers are hiding. Why the build year matters for the wiring harness you are buying, and why a stored car is worse than a used one. The viewing in eight steps, including the cold-start moments that come only once. The sentences you say to the seller, and how to build an offer out of what you found.
And a card you print and take with you — twenty-one lines, in the order you do them. That comes as a separate file, because nobody wants to print a whole guide to take a few pages to a car park.
This is what one of the twelve looks like
1 · The sills and the jacking points, under their covers
Two or three days · at worst, in a bodyshop; nothing at all if you look in time Chapter 5.1. The one item here that can turn structural, hidden behind plastic that clips off in a minute. There is no symptom, which is why it has to be a question and not an observation.
Now, before you travel — ask permission to unclip the covers.
And this is how the card reads
- Standing, before you start it
- Running
- On the move
What €24 buys, put next to what it saves
The sills and the tubular jacking points corrode under plastic covers, unseen, for years — and if they have gone it is two or three days of bodyshop work on a car otherwise worth ordinary money. It is also free to check: the covers clip off in a minute. The guide is €24. It will not stop any of that from being needed — but it does tell you which of them you are looking at before you agree a price, and that is the whole of the difference between paying for a car and paying for someone else's postponed maintenance.
Why there are no prices in it
Because a price we cannot verify is worse than no price, and because a price would be wrong for most of the people reading this anyway. Workshop rates across Europe differ widely, and so do parts prices. A quote from a specialist in one country tells you nothing in another.
What does not change is how much work a job is — that follows from what has to come off the car. So every point in the guide says whether it is an hour or two, half a day, a day, two or three days, or a week or more in the workshop, with a labour figure where a source gives one. And it says whether the money sits in the part or in getting to it, which is what lets you tell a fair quote from a bad one.
If you want a figure, ask any workshop one question — what is your hourly rate? — and every effort level in the guide becomes your own number, in your own currency. One question, and the answer is actually true for you.
How this guide was put together
Because you should know before you pay for it.
- Every fault and symptom comes from a source the guide names, the manufacturer's own documents first. The effort levels are our assessment, unless a source gives the hours.
- The guide says plainly where the money on this car sits — under the sill covers, in the roof hydraulics, in the engine loom and in the gearbox electrics — and which two engine items are worth asking about.
- The effort of every job is counted item by item and checked against the list before every edition.
- It says as plainly what you can leave alone as what you have to do. None of the twelve age points start from leave it.
Leave your email address at the checkout and both files arrive straight away: one guide and one card, as two pdfs. No subscription, no account.
The full guide · €24
16-page guide, A4 and phone · 2-page inspection card · instant PDF · VAT included
Have every car inspected before you buy by someone who knows this engine. This is general information about the model and not advice about a specific car.