For all practical purposes, the motor is integrated into the regulator assembly, there are no open gears that allow easy motor replacement like in many other cars. There are 2 steel cables in there that are wound onto a plastic spool. Once the cables start kinking (crunching), they don't wind onto the spool correctly anymore. The cables would have to be replaced, and the spool may be so damaged that even new cables wouldn't work correctly (new spools are not available).
It is a challenge to repair these regulators. Having a cache of spare used parts is required since none of the parts that usually break or get damaged are available new.
Buy a rebuilt regulator assembly if you can rather than one advertised as just used. They are all used, but the rebuilder repaired broken items, and probably repaired/re-enforced parts that eventually break. James Whitt at jewhitt2005 at yahoo dot com is an accomplished rebuilder... Chris