The locknut on the end is to adjust for "endplay" in the motor armature. Too tight it binds, too loose it wanders causing possible problems with the motor brushes. Exactly which gears have you determined to be OK? In all you have the worm gear teeth on the motor shaft, the outer teeth on the gear driven by the worm gear. Then there are the small gear teeth you can easily see on the main gear and finally there are the teeth on the regulator sector arm. Never saw a worm gear go but several times I have seen it rip out those teeth along the edge of the main gear. The main gear is about 3" in diameter and just lifts out of the motor assembly.
Try this site.
DIY Power Window Repair - Replacement OEM-Quality Window Motors, Window Regulators, Power Window Swithches, and Power Window/Regulator Repair Parts