FWIW, every time I've noticed excessive wear, I check and something is out of alignment or one of the pulley's is starting to drag. Go under, remove tension and see if everything spins freely and alignment is correct.

I vote bearings also. I replace at least one every year.

Well I've found the issue on the Allis. The idler pulley bearing was intermittently freezing up and caused it to turn on the spacer. Replaced the deck belt with a new kevlar belt and did the same for the drive belts on the Bolens. We'll see what happens.

when razor sharp knives cut through the air on a healthy bearing supported belt with a good pto clutch it has a unique hovercraft sound. A pure pitch of a note of sound if you will let me say it that way.