We have a mainshaft pulley that is 3 stacked on our 6-354. The belt went out while on passage in the middle of the night and I installed a new one. Unfortunately I put it on the middle pulley instead of the correct one (aft). The belt went out a week later. I put two new belts on it before I realized what I had done almost a month earlier and switched it back to the aft pulley after giving it a good eyeball for alingnment.

I was fortunate to have all those belts and was on my last one which is still working. I did purchase another backup ASAP.

Dumb,,, but it looked correct .