From what Im beginning to understand, the wiper becomes stuck due to rust, corrosion and lack of grease. this will eventually burn the motor out. The armature needs to be patiently freed with WD40, or other penetrating fluid, then greased so it moves freely with the glass up (not engaged with the motor drive gear)
start there, then see if the motor still works.
Heres a diagram: look at part #10....
Its best to get that part out of the car....I can look up how to do that if you cant figure it out.