Hi I cleaned a window motor in the past and it worked well, that window hadn't worked in years.
Take the motor out of the door.
On the end of the motor opposite the gears there is a retention method.
I say it this way since I can't see what you're working with. On the one I did (from 85 chevy) some metal from the housing was formed into tabs and then bent over the end to hold the cap in place.
Once you figured out how to loosen the end slowly take the cap off. You should see large chunks of graphite attached to springs. These are the brushes. The part where they touch the motor is the shaft for the motor. Dr Locke knows the correct term for that shaft. Use some contact cleaner on the shaft where the brushes hit. Clean it with a scotch brite pad to get the dark oxidation off, or at least reduce it.
When putting it back together you will have to figure out a way to hold the brushes back from the spring tension in order to get that shaft back in between them. Many times there are hole in the end cap to stick some unbent paperclips or whatever down in there to hold them. Then after you get it back together you can pull the clips out and the brushes will snap back against the shaft were they are supposed to be.
I used a wrench for the motor bolts, screwdriver, cleaner, q-tips, and maybe a scotch brite pad. Took about an hour. If you get stuck post some pics.