if you do not need the car - pull the roof out and give is a GOOD clean. most of the damage will be from build up of crap.
it will involve pulling the whole lot down to nothing to clean it BUT it will run a lot better once you have done so.
as for the motor you can still get them new from nissan (or from me) for about $600 or so. reconditioning one - find someone that does power window repairs (google pow win in nudgee qld ) as they did the recon'd on mine. happy to help you if you want send the motor /switch gear to them up here. I will lend them my roof to use for loading the motor down.