Idon't think there's much with the regulators to go wrong, it's usually dried up grease or the window not being adjusted properly putting more stress on the motor then it's made for.
Is it the gear going or the round roller things? They're supposed to be sacrificial but some of the newer kits I've seen they're solid which would put the stress onto the gear.
The so-called bushings? Yes, with some pressure. The other kits came with the bushings and gear already assembled.
And I agree with you on the regulator. These older ones aren't like the newer ones. Basically just a metal pair of scissors. Seems tight at the hinge point and I don't feel any teeth missing. I cleaned out old lube and re-lubed the first time around.
