I've got my horror story too, I too replaced my motor took the old one to Grainger and got a exact match, all was good till i tried to take the blade off the old motor when I dropped it. Fucked the balance all up. Took me not exaggerating 6 hrs to bend it back into balance using trial and error, even then it had a slight vibration to it. Well eventually it went away then about 2 years later I decided to blow the furnace out. The vibration returned come to find out the dust on the blades was balancing it. .lol. I figured it would eventually east the bearing up on the new motor but that was 7 years ago, I just lightly clean it now.