I have frequently observed the "creeping" input pinion needle bearing race when inspecting final drives.
This problem, in its end stages, is known to destroy a FD by wearing through the housing and interferring with the speedometer sending ring in pre-2002 final drives, or the tapered roller bearing in post-2002 final drives.
I have speculated that the creeping of the bearing race might be due to lack of a proper interference fit between the race and its seat on the pinion shaft.
This is the first time I have seen a complete lack of interference fit allowing removal of the race from the pinion shaft with finger pressure.
This suggests to me lack of an interference fit is the cause of this problem.
Anytime a FD is rebuilt, this problem should be looked for. The creeping input pinion needle bearing race can be identified without disassembly of the input pinion assembly, however, to correct the problem requires that the pinion shaft be removed from the housing.
This is from a pre-2002 final drive. I'll clean the surfaces and seat the race with Loctite 660.
BTW this was an incidental finding during rebuild following a classic crownwheel bearing failure due to over-shimming by approximately 0.15mm