Finally got some time and opened up the housing. The 3 nylon plugs are in perfect shape, not even scratched. I also took apart the motor and everything is in great condition, the brushes are still nice and thick. What do I do from here?

if the gears are not missing any teeth, then the motor isn't the problem. But just to make sure, plug it back in (just electrically) and make sure it turns when the window switch is pressed. next, check the gearing on the regulator to make sure it's not stripped. If it is, there's your problem and the regulator needs to be replaced. if the cables are not connected to the regulator (top or bottom) then it needs to be replaced. if it's the older angled/sliding X-bar, you'll need to find out what part is slipping and replace the rivets/bolts or the entire regulator.