After a bit more investigation on the window I am of the believe that the external horizontal seal is the major culprit.

On the coupe the window can be operated with the door open and as it has no window frame this friction can be discounted.

I have noticed that the external seal is quite deep. It also has the longest and most consistent contact point to the surface of the glass. The coupe door is longer than the sedan door as well.

In trying to clean my seal I noticed that it is very dirty and heavily impregnated with filth and grime. I was able to remove a lot of this with a rag over a plastic knife carefully running along the seal.

I would suggest that replacement of these would make a major difference.

Does anyone know how it is done? Does the anodised trim piece have to come off?

89 300CE
146k kms