Are your windows not coming all the way up, or are they having other problems?
I have rebuilt the rear motor nylon internal gear pieces (whatever they are called) in the 1989 GT Convertible that I gave my daughter. The windows haven't been used in such a long time they didn't work right when the car came back from the top-shop so I am going to have to pull them out again or look into what might be wrong with them now.