"Crunching" seems to be asking for little shards of junk to go into the bearing. Hard to see by eye, but under a good microscope its instantly visible. When customers return scanners for a replacement mirror they broke I routinely change the front bearing and sometimes tell them I won't replace their mirror unless they authorize the front bearing replacement because of all the shards i can see in the mirror
Heat is definitely the way to go
Sincerely,
Ryan Smith
ScannerMAX Mechanical Engineer
ryan {at} scannermax.com