Don't know if this is your problem, but it is an issue I ran into reassembling my doors after repaint. The bolts that go into the window frame connecting it to the door are 2 different lengths 12mm (#5) long and 16mm (#4) long. if you install the 16mm bolts in the upper position at the rear edge of the door, the extra length will bush the felt window seal forward against the window and cause excess friction.
