Thanks but I have already cleaned the space between the glass and the rubber (see my other post). I think its related to the actual rubber getting wet.
W140 S320L, 1997, Black with Black Bird's Eye Maple trim
Used GTechniq T1 on my window trims, no smearing, but then again I haven't applied it to the inner edge which touches the window. If you are going to do that, try a small area first to check for smearing, just in case...