Which runner are you talking about, the top one?, if it is the wheel is worn and you can buy new ones from VW heritage etc, you can tell if its worn by pulling the door in and out whilst open, it shouldn't move too much if it does its worn, you could also try adjusting the top bracket, 2 screws under the cover, undo them and see if you can push the bracket up a bit and then retighten.
If the bottoms coming out then it sounds like you need a new bottom runner complete, harder to find and more expensive, is it LHD or RHD?