My 86 190E has the exact same problem also. I just got mine out yesterday and put the battery back into it (I dont use it in the winter) but AW, I was going to ask the same question. Where do we need to start looking for the root(s) of the problem?
1986 190E 186K (For Sale)
(Maroon, Tan leather)
1996 C280 Sport 208K
(Brilliant Silver, Black Leather)
2002 CLK430 Sport 45K
(Brilliant Silver, Gray Leather , Birdseye Maple)