The pulley fitted to the front of the crankshaft is also a vibration damper: a rubber insert connects the outer ring to the inner one. The rubber ages and hardens, in the end it separates, and then the outer ring slips. The rubber ring can also fall out into the engine bay. This is one of the known faults of these engines, mainly on the early production units. The first sign is unusual vibration at idle, then a wobbling, clacking noise from the engine bay. If the pulley slips, it takes the belt drive with it and can touch the oil pan and the front cover. Those then have to be replaced as well, and the material cost alone is around 750 euro. Prevention is simple: it is worth checking the part number of the pulley and replacing an old-specification one before it comes apart while driving. The fault comes up above 170,000 km, but on the early units sooner as well.

The Mercedes 5 speed 722.6 automatic (5G-Tronic / NAG1) has three faults that also recur on the used market: (1) the control electronics sit inside the gearbox housing, and a leaking connector lets oil onto the electronics; (2) cooling faults around 2003 (and later) can let antifreeze into the ATF, which shortens its life; (3) wear of the torque converter lock-up clutch contaminates the valve body and causes jerky shifts.

The rear crankshaft seal ages and oil seeps at the joint between the engine and the gearbox. The telling sign is an oily, smeared bell housing at the bottom: if you see an oil patch there, the rear seal is letting through. The leak starts slowly and can contaminate the clutch or the torque converter as well. The repair is expensive because the seal can only be reached after the gearbox is removed. The part itself is cheap, the labour is not: even in practised hands it is four hours. The fault comes up above 150,000 km, and according to a workshop that works on these engines a fully tight example from this era is hardly ever seen. The front seal of the engine is a separate part and also tends to let through; that one oils up the front of the engine, and its replacement needs the pulley off, not the gearbox.

The rubber insert in the harmonic damper on the front of the crankshaft ages and hardens. The damper's job is to absorb crankshaft vibration, and once it cannot, the vibration passes into the body.

The engine mounts wear early: failures below 100,000 km have been reported. The rubber or hydraulic insert of the mount tires out and no longer absorbs the vibration. The symptoms are vibration at idle in the steering wheel and the pedals, and a dull thudding when setting off and when braking. A worn mount also puts more load on the other rubber elements of the drivetrain. The part itself is not expensive, a two-figure sum. One thing is worth knowing about the check. The mount cannot be judged from below without removing it, so anyone who says it is fine from a visual look is not measuring but guessing. There is, however, a simple test on a lift: if your finger fits between the anti-roll bar and the front of the oil pan, the mount is still good. If it does not fit, or the bar is resting on the oil pan, the mount is finished.