When was the last time everything was lubed? If it was like mine, it was when it left the factory in `66! Before buying anything, I would try cleaning what you currently have, lubing everything up with lithium grease, then making adjustments where needed with the tracks, as these cars were not known for having everything aligned well from the factory. My aunt & uncle were the original owners of my Belvedere II, and I can remember as a kid, the rear windows not going down all the way, and the passenger door needed a stong arm to get it down. With cleaning, lubrication, and re-alignment of the tracks, all 4 windows now function as they should...no parts changed (aside from worn out weather stripping).