[ericn1300]

there is a slot on the outside rear of the door about halfway up where the rear roller runs on the outside towards the rear that's often ovelooked. since it's exposed to the elements it gums up pretty fast. i got mine working good again by spraying inside the track with foaming liquid wrench first to clean the track and free up the roller, worked the door back and forth a few times, then applied white lithium grease with a Qtip to keep it moving freely. the front top and bottom rollers and traks are pretty easy to find

I don't know how old Old Master is but his advice is right on. my 1950 GMC manual specificaly recommends "oiling the door and hood hinges, a routine maintenance that service stations often overlook"