I pulled the 1/4 window motors out of my 89 convertible early this year.
One was not working.
Both motors were really in good condition, even the brushes had plenty of life.
They did need cleaning up.
I think the one that stopped was a problem with the rubber spider.
After some TLC both motors work fine.
If you go back to the following thread starting about Apr 15 there is info on the issue.
Quite possibly nothing wrong with your motors once cleaned up and the rubber spider
put back with suitable rubber grease.