On the road
All R129s should feel lively and under-stressed on the road, especially V8s and V12s. The sturdy V8s are the most dependable, usually suffering only minor ailments. An M119 sounding tappety is likely to need new plastic cam oilers (c£600 to replace all 16), while poor hot starting on later M113s is usually a crank sensor: an easy fix.
Check that the ’box shifts smoothly into all gears (including reverse); the five-speed auto on ‘sixes’ can have issues getting fifth. Confirm that the oil and filter have been changed at least every 40,000 miles; for a while they were ‘sealed for life’ until Mercedes realised that was a mistake...
The suspension and steering should operate quietly and comfortably, with no knocks or sloppiness. It’s a heavy car, so dampers, bushes, suspension top mounts and steering box – and especially the idler – do wear, and springs break.
They’re hugely complex: the first cars had a remote-control rear-view mirror and autolocking door pockets, dropped in 1995. All had an auto-locking centre console and boot storage compartments, and ’97-on cars have three-way programmable garage door transmitters on the rear-view mirror, plus rain-sensing wipers. A separate electric water pump feeds the heater (and fails). ADS active damping was optional: it’s great, but needs an expert to sort it if faulty. Every aspect of the seats adjusts electrically (check heat pads, too), and hardtops are released and lifted electrically – impressive if it works! A weak battery can cause stray warning lights.