I've been using the Domel 492 vac motor. The brushes have been lasting three times longer than the cheapo GS that
Kleen-Rite used to sell. I haven't had one fail yet; some are as much as 8 years old which means the original (Lamb) motor only lasted three.
The 492 is a bit taller than the standard motors, but it will fit in most vacs as long as they're changed in pairs. If height is critical, they have another model that's an exact fit.
FWIW, I would have put this thread under the General section.