I have just replaced a vac motor on my Ninja.
I think the reason it went is because the pump had been leaking, much condensation inside the unit.
I removed the pump head from the body, opened up the head and carefully sealed the flange with sealant, now working a treat with no leaks.
Having changed to using powders from Chemspec 'formula 90' 9 months ago, I was concerned that there might be a build up in the pump but it was absolutly spotless inside.
I also cleaned the filters on the wand and found just the usual bits and fluff, no scum from powders.
John