Hi guys i have a small spot of condensation / dampness occurring in the rear drivers side window just at the B pillar



what would the issue be.

I havent taken the door panel off yet.

The only thing ive noticed is when it rains the {Felt} on top of the door gets wet no felt on the other doors gets wet.

My father in law also has this issue in the same spot.
His is a 2008 520d
Mine is a 2005 M-Sport 530i

Any help appreciated