MK, you can probably rebuild those window motors yourself. Compared to gasoline powered 'motors', DC electric motors are easy to rebuild and there's a lot to be said for a rebuild that can be done on your kitchen table with (mostly) hand tools!
There are the bearings or bushings on the ends of the rotor- usually standard thruout the world. And the carbon brushes- also std, which are quite easy to modify with a file for particular dimensions. I once fixed a DC motor with a brush made from the carbon center post of a discarded 'C' battery and a nail file. Then you cut the commutator the brushes run on flat to eliminate wear, then square each commutator block so the insulated gaps between blocks are sharp and even with no burrs. That's about it as long as there are no shorted windings.
But modifying DC motors for more rpms or torque is extremely difficult and involves changing the windings. If you're not satisfied with stock performance, you WILL need a pro electric motor shop. Try it.