Despite the indestructible reputation, owners identify recurring service items: periodic valve adjustments, a timing chain that stretches and should be inspected around 150k, and motor mounts that wear roughly every 50-60k miles (the five-cylinder rocks at idle when they go). The chain is hydraulically tensioned and considered straightforward to replace.
Engine service reality: timing chain, valves, motor mounts
Mercedes-Benz W123 · mechanical