Most buyers spend hours researching a classic car online and 45 minutes looking at it in person. That ratio is backwards. The viewing is where the money is made or lost — a thorough check on a car with hidden problems saves you from a financial disaster; a thorough check on a genuinely good car gives you the confidence to pay the right number without hesitation. I've seen people walk away from solid cars because they weren't sure what they were looking at. I've also seen people hand over serious money for cars that needed more spent on them than the purchase price. This checklist is designed so you're not one of those people.
This is a used car buying checklist designed for classic cars specifically. For model-specific details — where a W124 rusts, what a W126's self-levelling suspension should do — use the individual buyer's guides alongside this.
Note on the printable version: The one-page field version of this checklist — designed to be printed and taken to a viewing — is included in the full ebook. This article covers the reasoning behind each stage so you understand what you're doing and why.
Stage 1: The Phone Call
Before you drive anywhere
What to ask before you go
- Why is it being sold?
- How long have they owned it and where was it kept?
- Is there a service history — stamps, receipts, or both?
- Has it been in any accidents? Any bodywork repairs?
- Does anything on the car not work as it should?
- Can you have it inspected by an independent mechanic before buying?
- Is the price negotiable?
A seller who answers these questions directly and without defensiveness is a better starting point than one who hedges or rushes you. If they say "I don't know" to every question about history, set your expectations accordingly. If they say an independent inspection is not possible, you already know what you need to know.
Stage 2: The Approach
First impression, from a distance
Before you touch the car
- Is the car sitting level? A car that sags at one corner has a suspension or structural problem.
- Are all the panel gaps even — bonnet, doors, boot? Uneven gaps point to accident damage or poor bodywork repair.
- Does the paint match across all panels in all lighting? Overspray on trim or different texture panels suggest respray.
- Is there visible rust bubbling anywhere on the exterior panels?
- Do the tyres look even on both sides?
Stage 3: Exterior and Bodywork
Walk the entire car
Bodywork, glass, and trim
- Run your hand along each panel — feel for filler (a ripple or slight flex under pressure).
- Check all glass for chips, cracks, or delamination of the heated rear screen.
- Inspect all rubber seals — door seals, windscreen seal, tailgate seal. Cracked or missing seals mean water ingress.
- Check the wheel arches — reach inside and feel the inner lip for rust perforation.
- Inspect the sills with firm thumb pressure along the base — hollow or soft means rust behind the outer skin.
- Look at the shutlines on boot and bonnet — they should be even and match the door shutlines in quality.
- Check the spare wheel well — lift the boot mat and look for rust or standing water evidence.
Stage 4: Underbody
Get underneath — this is the most important physical check
Structural and mechanical underbody inspection
- Check the floor pans for rust or perforation (press with thumb — should be solid).
- Inspect the rear subframe / axle carrier mounting points (critical on W124, W210, and all ageing classics).
- Look at the exhaust system — condition and mounting.
- Check for fresh underseal applied over rust (common concealment tactic).
- Look for evidence of previous accident repair — welded seams in unusual places, mismatched metal finishes.
- Check the front subframe and control arms for damage or heavy corrosion.
- Look for fluid leaks — oil, coolant, hydraulic fluid.
Red flag: Fresh underseal applied to specific areas of the underbody — rather than uniformly — is a common way to hide rust. If you see a patch of new black underseal surrounded by old, grey, undisturbed underseal, investigate what's underneath it before buying.
Stage 5: Engine Bay
Cold engine, before it's been started
Engine bay inspection
- Check the oil level and condition — pull the dipstick. Dark but not sludgy is normal. Creamy or metallic particles are bad.
- Check the coolant level and condition — the reservoir should show between min and max. Look for oily sheen on the coolant surface (head gasket concern).
- Look for evidence of recent leaks — oil staining on the block, dried coolant residue around hoses.
- On classic Mercedes: inspect the wiring loom — gently squeeze the insulation. If it cracks, the harness is degrading.
- Check the battery terminals for corrosion.
- Look for signs of crash damage repair in the engine bay — misaligned panels, paint where it shouldn't be.
Stage 6: Cold Start and Warm-Up
The most informative five minutes
First start of the day
- The engine should start cleanly without excessive cranking.
- Note any smoke from the exhaust on cold start — brief white vapour in cold weather is normal. Persistent white smoke (coolant), blue smoke (oil), or black smoke (rich fuelling) are concerns.
- Listen for any ticking, rattling, or knocking on cold start that clears within 30 seconds. A rattle that doesn't clear needs investigation.
- Watch the temperature gauge — it should rise steadily to normal and hold there. An engine that reaches temperature and then continues rising has a cooling system problem.
- On diesel engines: note glow plug pre-heat time and starting behaviour. Difficult starting on a cold diesel points to glow plugs or injection pump.
Stage 7: Interior and Electrics
Test everything
Interior condition and function
- Test every window (all four, including the rear quarter windows if fitted).
- Test all door locks from inside and outside each door.
- Test the central locking from the key — all doors should lock and unlock smoothly.
- Test the climate control — all fan speeds, temperature control, vent direction, and defrost.
- Test the sunroof if fitted — open, tilt, and close.
- Check all warning lights on startup — they should illuminate and clear except any genuine faults.
- Pull back the carpets and check the floor for dampness or rust (particularly under the front footwell area).
- Check the headlining for sag, staining, or damp marks (indicates roof seal leaks).
Stage 8: The Test Drive
At least 20 minutes — include motorway speed and a firm braking test
What to assess on the road
- Brake firmly in a straight line at 30–40 mph — the car should stop straight without pulling.
- At motorway speed: the car should feel settled, not wandering. Any instability points to worn suspension or alignment issues.
- Through corners: no clunking, no vagueness, no rear instability. Clunks from the rear over bumps need investigation.
- Test the automatic gearbox through all positions — no slipping, no harsh kickdown, no hesitation when pulling from standstill.
- Check the temperature gauge stays stable throughout the drive.
- On return: check under the car for fresh fluid drops. Any new puddle is a leak to investigate.
Stage 9: After the Drive
Final assessment
Before you make a decision
- Review your notes from each stage. What needs money? Is it priced in?
- Check the VIN against the registration document and any other documents in the car.
- Ask to see the service history in full — stamps, receipts, or both.
- If anything significant came up in the inspection, get a quote from a specialist before committing.
- If the seller won't allow an independent inspection, walk away.
A car that passes all nine stages cleanly is a car you can buy with confidence. A car that has issues in stages 3 and 4 (bodywork and underbody) needs those costs priced into what you pay, or walked away from if the seller won't negotiate. Mechanical issues in stages 5–8 are usually more straightforward to quote and price — bodywork and structural rust are not.
Want model-specific checklists?
The full ebook takes this process and applies it specifically to the W123, W124, W126, 190E, R107 and R129 — with a printable one-page field checklist for each model.
- W123, W124, W126 S-Class
- W201 190E, R107 SL, R129 SL
- 68 pages — printable inspection checklist included
One-time purchase · instant download · 68-page ebook plus the field checklist