Similar to my Silverado's rear axle bearings that I have to change every few
years...because I have 1 ton coil helper springs on the rear axle. That I over load
it every year during firewood/wood-pellet season. Many times loaded up to around
2.4K-3K of wood in a half ton (6.2K GVWR & ~4.25K RGAWR)
Most times the cage is mangled similar to this picture and other times one of
the rollers are out of the cage and the rear end starts to make a 'noise' because
there a roller missing. A looooong magnetic tipped retriever gets the roller
before it gets to the diff
If the castle nut was loose, then think it allowed the shaft to move laterally
and one roller took a new rout to deform the cage...or as someone stated...maybe
during assembly...will never know...unless this repeats...