I saw some research (on line) once that said the reliability of the C classes started to drop in the mid 90's. Now this doesn't mean they are not reliable, just not as reliable as the ones before. They are still more reliable than american cars , but not japanese.

Definitely stay away from the new body versions (2000+) of the c class-lots of problems. Pre 1996 C classes seem to hold good reliability. Consumer reports also has shown a decline in reliability in the c-class starting in the mid 1990's, and it bottoms out in the years 2001-2002. although it is hard to tell yet, the 2003 and 2004 models are improving.

As far as the engine - go for the 280 6 cylinder -nice power, fuel usage is between 25 and 30 mpg depending. This is what I measured on my car, so it is not a guess.

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1977 280 E
1994 C280
1992 190E (sold)

"Jump in the hatch and turn on the key, pop in the clutch and let the wheels roll free"