Joe Boulay 1/21/2013Hello
Usually what happens is the rollers go bad and bind horribly. Also the rear center hinge assembly seizes and binds to make matters worse. Unfortunately I would suggest that you at least get one side repaired first then the other when you can afford it. after they are repaired make sure that you keep the hinges,rollers and guides lubricated and at the same time free of grit . Hope this helps.
Automotive Technician & Author