Another thing I'll bring up is what commonly causes the death of these regulators is the glass sticking in the felt window guides. It seems like the slightest little snag can send a regulator on permananent vacation. While you have the door apart to replace the regulator, spray the living daylights out of all the felt guides you can see/feel inside and outside the door with some good type of dry lube. I was able to make all 4 of my GP doors actually roll up/down with some respectable speed and now don't hear any slow spots on the way up like I used to.
