ours (2005) just rolled 61k, and seems to be getting better MPG now, than at 40k
its a beast of a car (I've gotten 3 speeding tickets in it) there are a few at Mercedes Benz of Cinci that we've looked at (as an addition) right now and the prices seem to be coming WAYYYY down for a 50k mile car
only problems we've had,
~leaky injectors around 15k miles
~bad xenon headlamp starter
~power trunk closer was slamming shut
~some distortion in the Harmon Kardon speakers (amp was going out)
all of the above were covered
SBC brakes, take ages to shut down = increased labor costs
we had to do front pads, and an oil change and it came to like $600
aside from that, the only quality problem i've noticed is the W211 wheels...
seem to be poorly painted, and chip/flake/pit and tend to look like $h!t
and I actually take care of ours!