Funny I haven't seen this post earlier, because I have had the same problem on our 93 190E 2.6 and it hasn't been getting any better or worse. We thought its been like that since the first time we took it out in winter (in early 97) and the wheels were slipping like crazy. We thought that it might be due to excessive wheels spin. As for the dealer, they haven't been able to find a problem with the car, and everything checks out fine. They did say that other 190E owners have experienced the same thing though, and they thought it might be like that since the factory built it.
I sure would like to find the answer to this one if there is any.
Chirag (Charlie) Patel
99 Mercedes-Benx ML 430 V8 w/custom TV, Video, UHF, speaker system
93 190E 2.6 (4-sale) w/ an amp, equalizer, and CD-changer, integrated w. stock stereo for integrated cellular phone speaker system
2001 C-Class - Maybe (if 190E sells