1. replace the hinges... old one may be sagging or too loose
2. replace the seal... no idea where you'll find one, but make sure your using the original seal for your door
3. car handles... replace the entire mechanism, some parts (inside) are plastic and may be loose
4. replace the entire mechanism of the windows... same reason as the car handles...

I did the same in the 90's for my box type... almost everything inside the door was replaced! sadly, my wallet only allowed me to fix the 2 front doors