I've owned one since new. My experience is good, it's a nice driver
particularly on the freeway, expect 26 mpg there. My car has now gone
33K miles; my experience is:
The engine's valve cover and front seal leaked oil and were replaced
under warranty at 18K miles.
This straight six has an iron block and an aluminum cylinder head which
expand and contract at slightly different rates; that strains the
cylinder head gasket so it seems to fail after 150K miles.
The car has quite wide tires, IMHO, which are sensitive to incorrect
front toe-in. When the toe-in is incorrect the tires wear and the car is
a bit "squirmy" on uneven local roads in the sense that it doesn't glide
ahead quite straight but a bit in a zig zag motion as the uneven roadway
exerts more or less force on each front tire. It's a minor point, more
of a symptom of incorrect toe-in than "a problem".
If you buy one you should know that the paint is water based and the
layer is thin. At the factory they told me to wax it but not polish it
for the polish would wear the already thin paint layer.
Finally, there was a recall for the side airbags to be modified, suggest
you check with MBUSA that this was done before you pass the cash.