Jimtoo mentioned using a repair shop. . .
We have such a place here in San Angelo and a friend with an SOB had his main slide motor repair. The shop actually repairs and/or rebuilds only DC motors and most of their business are things like alternators and starter motors. They said sometimes it can be hard to get parts for specialized RV motors, but more often than not they can repair it with generic parts (e.g., brushes, etc.). Anyway they charged him around a hundred bucks, took them three hours, and they told him it should last another five years. We have another shop in town I have used, but they only work on a/c motors. I guess it is common to specialize in d/c or a/c motors.