W108/W109 Buyer's Checklist: What to Inspect Before You Buy a 1965–1972 Mercedes S-Class

The W108 (and its long-wheelbase, air-suspended W109 twin) is the S-Class before it was called that: built 1965–1972, on a 108.3 in wheelbase in standard form and 112.2 in for the SEL cars. Engines run from the carbureted 250S six at about 130 hp to the 300SEL 6.3's M100 V8, 250 hp DIN in a car that weighs about 4,020 lb and was the fastest production sedan in the world at launch. The guide's W108/W109 data reduces the buying decision to a short list of inspections. Rust and identity come first; everything else is a budget line.

1. Sills, floor pans, and the trunk floor

The guide's buyer's checklist leads with structure. Poke and tap the sills and rocker panels along their full length and look for filler: they are structural, and a proper repair is expensive. Lift the carpets and check the floor pans under the seats and pedals, where pooled water rots them. In the trunk, check the floor and spare wheel well for dampness, pinholes, and seam rust; leaking seals are common there. Holed floors and a badly rotted trunk are dealbreakers on the checklist. Rear wheel arches bubble at the lips because mud traps moisture behind them; that one is a budget repair, not a walk-away. Crushed or rusted jack points are a warning sign of prior damage or deep rust, and cracked or collapsed front subframe mounts are a dealbreaker if torn through: they affect handling and safety.

2. Kingpins: the wear item every W108 has

The front suspension is a double-wishbone design with kingpins, and the guide's spec table carries the maintenance rule in plain language: grease the kingpins at every oil change. On an inspection, jack the front axle and rock each wheel top-to-bottom. Play means a rebuild; the checklist calls kingpin wear a normal wear item to budget rather than a dealbreaker. The Common Fixes tab prices a kingpin kit at roughly $200–400 in parts and lists the symptoms of worn ones: steering wander, clunks over bumps, and uneven tire wear.

3. Air suspension (W109 and every 6.3)

Long-wheelbase W109 cars, and all 300SEL 6.3s, ride on air suspension instead of the W108's coil springs. The checklist test is simple: the car should sit level after parking overnight, and you should note how often the compressor cycles. A car that sags after parking with a compressor that runs constantly points at leaking bellows or a tired valve block; the fix in the guide data is to soap-test the bellows and valve block, rebuild the valves, and replace the bellows. The checklist marks a collapsed system as a dealbreaker, and the parts are priced accordingly: bellows, valve seals, and an air dryer, at the guide's top cost band.

4. Engines: head gaskets, and the M189's injection pump

On the M130 six (280S/280SE), cold-start the car and check for oil and coolant mixing and valve clatter; the guide flags M130 head-gasket seeps (a coolant weep at the head/block joint) as a known fix, gasket replacement with a head-flatness check. The injected cars run Bosch mechanical fuel injection, and rough running on them is worked through fuel pressure, the warm-up regulator, and injector spray before anything else.

The rare 300SEb's M189 six has the single most expensive failure point in the whole guide: its Bosch mechanical injection pump. The Common Fixes tab puts a professional pump rebuild at $1,500 or more, with parts scarce, and notes that low oil in the pump itself accelerates wear, so check the pump's oil level and ask for pump service history. The checklist treats pump condition as a strong negotiating point.

5. Verify the car is what the badge says

This matters most on the 300SEb (1965–1967): only about 2,737 were built, against 55,000-plus 250SEs, and the guide warns that many are mislisted as a plain 300SE or 280SE. The identity checks are mechanical: the chassis plate should read 108.015 and the engine number should start with 189. The Common Fixes tab carries a whole entry for the misdiagnosis, because the M189 and M130 share virtually nothing internally and wrong parts get ordered. Two more identity traps from the checklist: a genuine 300SEb runs on steel coil springs and never had air suspension (if it has air, it is a W109 300SEL or a modified car), and its rarity premium has to be priced against M189 running costs, which run several times higher than the common sixes. On any 6.3, the checklist is blunt: no service records, no deal; rebuild costs are enormous.

6. Paperwork and the small stuff

Matching numbers, service history, and a clean ownership chain protect the car's value; the checklist marks weak paperwork as a warning, not a footnote. Beyond that, the known fixes are mostly budgetable: vacuum door lock leaks (a hand vacuum pump finds them; weak locks also slow engine shutoff), a dead heater blower (dash access, medium difficulty), steering box free play (adjust per the manual, rebuild if worn), and rear axle carrier clunks on acceleration and deceleration (subframe and carrier mounts).

Open the full interactive W108/W109 guide for the complete buyer's checklist, common fixes with costs, stock specs for every model from the 250S to the 6.3, and current for-sale listings.

Compiled from the Cerch Garage Mercedes-Benz W108/W109 guide (Buyer's Checklist, Common Fixes, and Stock Specs tabs), which draws on W108 community references and workshop manuals via classicjalopy.com and owner-community consensus. Production figure for the 300SEb from encyclopedia.pub data as cited in the guide. Prices and costs are as listed in the guide and change; verify before buying anything.