We had an old american Gisholt capstan lathe that used 6 B-section belts. The tensioner ran on the back of the belt and after 6 months the belts started breaking up. It took about 6 hours to change out and was not a cheap operation.
We found a bit of paper stuffed in the cover from a fitter in Cleveland, Ohio that showed he had been replacing belts every six months as well! There was still a plate on the headstock that said "This Machine Conforms to Orders of The War Production Board"
We replaced the belts with notched belts and when the company was sold seven years later the belts were as good as new.
I recently bought a Warco pillar drill and it suffered from a lot of vibration when running. Replacing both belts with good quality notched belts transformed the drill, a totally different machine and a pleasure to use!