I bought my 89 300E two months ago and I LOVE IT! (just my $.02)
I get around 20mpg in town (I have a short in-town drive to work) and around 24mpg on the highway if I go more than 70miles +-. I don't race it much, so that helps.
Mine is a cherry and I'll to my damndest to keep it that way. I had the cruise control amp go out on me (I'm quoted $325~ parts and labor at a local MBZ repair shop; not dealer) but other than that nothing to complain about.
1989 300 E
1992 190-E 2.3