Opened the 14-Bolt, Found Some Bearing Parts...

[Rufton]

The pinion support bearing retainer can be a pain to remove even on bench. Sometimes it isn't even removed during rebuild. Looks like you'd have to remove retainer (not easy) then install bearing then install retainer (not easy).

I can only guess the bearing fell off during pinion install and "mechanic" failed to notice/care.

I'd have a hard time trusting "mechanic" rebuilt everything else to spec; I'd disassemble, inspect and reassemble to spec.

I've seen warped pinion shafts so I'd check pinion run out.

Looks like gear oil is milky in photo. If so I'd check all bearings and races for pitting.

I didn't see any glitter. Did any of the recovered bearing parts get ground up?