well there is a 190 forum...
www.190revolution.net
I own a 190E 2.6...a 1993 model with 193,000 miles on it.
I came across a thread on the rev (190 revolution) that had a break down of the most troublesome systems on the 190..i cant seem to find it but the most trouble some was the climate control/air conditioning.
Personally, I love the 190 series. For as small as the interior is there is plenty of room for 2 people. The trunk size is ample but not as large as the S-class (i also have a 300SD).
Since I purchased the 190 I've had to have the a/c recharged. The 190's a/c is R12. I've had to have the hydraulic lifters (compensators) replaced and a rear brake job. Other than that I havent had much trouble with the car.
Some thing i've read...this is only what i've heard how accurate the data im not sure..someone else here can verify (this is for a m103 based 190 2.6)
The lifters need to be done around 150k or so.
The valve guides sometime after that
the transmission might be weak and should be rebuilt near 200k
check out the rev. they're a helpful bunch..
kris