It's interesting because I've had exactly the opposite experience. I'm on the benzworld forum, know people that drive them. The general opinion is that their electrical systems and transmissions are weak links, but other than that they're solid through the 90's. My uncle has a late 90's SL that's around 300k miles and absolutely looks and drives like new.
I believe you they are out there I would say the newer ones seem pretty good, but time will tell, its a 2011 s550. Keep in mind all of our cars are california cars so good weather year round no ice or salt, well taken care of.
Just to name one recent problem my friend had a 98 S430 I believe car didn't even make 110k miles without trans problems, electrical, engine, etc... Got rid of it got a 04 e55 and no issues, this was last year maybe around march 11. I have a lot of other stories but I guess a lot of mbworld people are lucky lol