Hi Don,
I use WD40 at the end of every day, but last year my blower locked up when doing the worst nightclub carpet I've ever seen, I only stopped to mix some pre-spray but the sugar from the muck in the carpet must have caramalised in the blower, and locked it solid.I flushed it out by taking the lid off the waste tank and putting a hosepipe to run through the vac inlet pipe as I turned the engine over! It worked great and not had that trouble since!
All the best
John