Difficulty Rolling Rear Windows Up or Down....

Hello Everyone,

I have in my possesion a 1973 Scamp. I've been doing some intense rust removal from the inside of the vehicle and really noticed for the first time that the rear windows have a difficult time coming back up once they've gone all the way down. It seems like once they've gone into the door panel, they get hung up on the way up. Anybody encounter this before and know of a remedy? Also does anyone know if they happen to sell any power window sets for the rear windows? I managed to find them for the front, but no success for the rear. Thank you all for the help in advance.