In a former life, having motors rebuilt was something I had done regularly, and curiously, in places as far flung as Bangkok and Brussels, and throughout the USA. For larger HP motors the cost was generally a fraction of what replacement was.
Fractional HP DC motors can also be rebuilt, but when a suitable replacement (maybe with some minor modifications) can be purchased for less than $100, rebuilding doesn't look so attractive--unless your comparison is that >$1K MB replacement.
For years, Bud's Benz (check vendor list) has offered a replacement, and it's in their catalog for $189 or so. I don't know if this is an off the shelf replacement (such as those listed by Tom and Alfred) or one already modified for a drop-in fit with no additional work necessary...but it is worth a look or a talk with Bud's.