I got my '67 from the shop this week. I had the rear axle bearings replaced. The shop said they had to machine one axle because it was damaged.
What gives? What is there to machine on an axle? Sleeve over the grove where the seal rides?

 

Ask them? I can't think of anything other than what you said.

 

B7TZ-4234-A (replaced B7C-4234-A) .. 9" Axle Shaft - Right/Left is the same / Obsolete

1957/67 F100.

 

Prolly where the seal rides. If the lube level was low enough I suppose it possible the axle bearing was freezing up a tad and spinning on the shaft. The bearings are supposed to be at a friction fit. And then the retainer collar is supposed to be a press fit. Possible, but not probable. Come to think of it, maybe they screwed the pooch and messed up so the retainer collar was too loose. Had to fix that.