Rust
Despite full galvanisation from 1994, the W202 is notorious for corrosion on the front and rear wheel arches, the bootlid lock surround, the door bottoms and the jacking points. The front spring perches can collapse without warning, so inspect them carefully. Cars from 1993 to 1995 are the most susceptible, and rust is the single biggest factor in whether a cheap W202 is worth buying.
The wiring harness
The biodegradable insulation used on M104 and early M111 engine looms degrades with heat, causing short circuits and misfires. A replacement loom is common and costs roughly £500 to £800; check the date stamp on the harness, and treat odd electrical faults as a likely symptom.
Mechanical checks
On the M104 six, the head gasket can leak oil near the timing cover; a documented replacement is a strong plus. Mass-air-flow sensors wear on all petrol engines, causing rough idle. Front lower-arm bushes, drop links and ball joints wear quickly, so budget for a suspension refresh by 100,000 miles. The 722.4 and 722.5 automatics need regular fluid and filter changes; the later 722.6 is more robust. Early ESP hydraulic units can fail expensively.
Interior and what to buy
Check for broken sunroof mechanisms, sagging headlining, delaminating door inserts and the known evaporator-sensor failure in the climate control. A rust-free car with a sorted harness is the goal. The C230 Kompressor and C280 are the value sweet spot, the AMG cars are the collectors, and a clean diesel makes a durable daily. Condition beats specification every time.