http://davebarnhart.com/mb300e/Buying.htm

Head gasket is a common issue, my '88 300E leaks some oil there (but not yet mixed with the coolant). I just continue to drive it.

AC/heater/blower issues seem to be a fairly common issue, as are power windows.

Overall though, they're reliable cars that can go forever with proper care/maintenance.

Mercedes love regular oil changes--it's ideal if you can find a previous owner who's done that.

Pricing-wise, it seems late 80s/early 90s E's go in the $2k-$4k range. Mine was $2000 with the known head gasket issue, and two windows that wouldn't roll up. Tan leather interior with a few cracks, but probably better than average condition. No cracks on dashboard, rear seat area looks new/like haven't even been sat on. Teal paint is nearly like new--ZERO rust! Broken odometer shows 105k; previous owner estimated about another 10-15k after it broke, so I figure they probably actually put 25k on it.

Good luck! Nothing like a good 'ol 300E.