Have seen several mentions of the S600 being a "problem" car. Just wanted to relay my personal experience, which has been the opposite. I own a 1994 S600 coupe with just under 45,000 miles. It's been problem free, is a joy to drive, to sit in and to look at.
I also own a 1991 300e. That's a good, solid car, but it's like driving a farm tractor compared to the coupe.