Just documenting things I’ve learned: The Bosch window motors used in the XJ-S doors 1990-on have an 8-tooth pinion gear. The same motors are used in Range Rovers and in the VW Golf 1990-1996.
A very similar motor, exactly the same except having a 10-tooth pinion, is used in many Mercedes and Volvos. So, if you find one in the junkyard, perhaps you can swap out the pinion gear?
The same motor is also used in the rear windows of the XJ-S convertible 1992-on, except that motor has a 14-tooth pinion on it. Again, perhaps pinions can be swapped around as needed? The 14-tooth version is also found in the Mercedes W123.