Just had the same problem on my 91 GL. Removed panel and disconnected motor
from the regulator. 3 easy bolts. Took the motor to the workbench and
completely took it apart. Found rust in bottom. Cleaned everything out with
steel wool and greased everything again. Seems to work ok now. Does not have
the same speed as it used to but it sure beats paying 250 for a new motor and
used ones are near impossible to find. There is hope. Good luck