Hey Kirby specialists, I have a bit of a dilemma with belts for my 516 and 519. When I restored these two machines a couple of years ago, I put in the new style brushrollers, and was advised to use the new knurled belts for them. I installed part # 301291. I've never worked harder making the belt lifter stretch these belts, and I ruined what appeared to be a perfectly good, original belt lifter. The back plastic tabs broke off under the stress. At that point, I had not heard of the Kirby soft grey belts - the online shop never mentioned them. Got a supply of them recently and just installed one this evening. They too are exceedingly stiff and put that red plastic belt lifter under considerable stress, but at least it didn't crack the tabs. Question: is this a matter of aging belts, aging plastic belt lifter, or both? I presume with some use that these grey belts will break in a bit and not be so stiff when turning the belt off, and for now it seems to be operating the brush roll correctly. Advice?