The best way to damage a Sanitaire is running with a slack belt, because a slack belt is like dragging your hand over a table, gradually the friction builds up and heats your hand to an unbearable level, and that's what causes the "blue pulley syndrome", aswell as the BananaGroomer issues (my C12 came with a bent brushroll, due to a severely worn belt being used)...
Okay, so maybe I didn't put it into the right terms, the Hoover belts provide better Traction, like how a set of chunky tyres on a 4x4 gives traction offroad, the RD belts are like using F1 racing slicks in a muddy field, they just spin and burn out, meaning little or no movement of the brushroll when set to the correct height for the carpet involved (for me I have my 8 position Dial-a-Naps set to "3", and the 6-position to "2" for the commercial-grade carpet in the living room), which causes the pulley to heat up, the brushroll's belt channel to heat up, and hey presto we have either a snapped belt or bent metal, coupled with the awful stench of burning rubber...
Another car analogy, when you have an engine with a worn belt screeching on the alternator pulley under the bonnet, is it overheating because it's too tight? Nope, it's screeching and overheating because it's too loose, causing, you guessed it, heat damage, pulleys turn a funny rainbow colour, the belt slips, screeches, smokes and finally snaps, and then your battery dies after a few miles cos you have no power from the alternator, or you end up roasting hot and sweating like a pig cos your A/C pump isn't pumping!! Fun eh?
Anyway, I don't know what they did to the vacuums since the original design for the Eureka upright, but they must have moved the brushroll back or the motor forwards since the 260 or 265 (I forgot which model it was that I was chatting to someone about) when they designed the Sanitaire series, aswell as the later Eureka upright series based on the same chassis & motor designs, and neglected to adjust the length of the belts, thus causing the problems of wobbly pulleys and brushrolls with a 6 degree bend in them, and this error is why I use the Hoover belts...
I know it seems like I'm being a pain in the rear with this subject, but, when it boils down to it, there is a flaw with Sanitaires that has not been officially rectified, and given how the production of them is in Mexico or some other cheapskate lazy-arse "That'll do" attitude country, it's doubtful it ever will be, and thus people like myself come up with solutions (although I did not come up with the Hoover belt solution, I was given that as a suggestion when I got my first Sanitaire) to problems nobody really sees because they're not actually looking properly, regardless of whether someone runs a vac repair business or worked in the R&D department of a vac company or whatever...
Anyway, I'll leave that there, I need to go to bed, was meant to go like two hours ago.... :S