For those that care, I managed to solve this problem by experimenting with several Hoover vacuum cleaner belts. One fit snug but when the motor revved up centrifical force caused the belt to actually lift free from the drive spindle. The belt is made of rubber, unlike the impregnated rubber weave found with the stock belt, and is designed to stretch substantially. (This tells you why the stock belt is designed to fit snug and not stretch much at all.) I eventually tried a Hoover belt that stretched and fit fairly tight and it worked fine. I am back to using the stock belt, but the Hoover belt is in my spare-parts box, ready to be used when the original belt wears out.
Howard Ferstler