I did mine this summer. I didn't have the inner axle seal. So a couple weeks later I did it again. Then I found that the breather was pluged and that is why the axle seal was leaking oil into the bearings. So now I need to do them again
So I will have done them 3 time in 4 mo
The rear wheel bearings in a full float rear are the exact same bearings as used in the front axle. They are often over-looked, myself included. I had over 100 k on mine before I did them . I think in future that I will do mine every 30k or so. I also intend to change the little seal in the end of the axle housing yearly.
Good question. When mine were first inspected at 100k, there was no grease at all in the rear wheel bearings. None. There was a small amount maybe 1/4" thick in the hub cavity. The good news is that the hub seals were leaking and there was plenty of gear oil in there so the bearings looked good and were well lubricated.
If the PO had let the rear diff oil level get too low the bearings would have been dry and it would probably toast all 4 at the same time. I plan to take another look this spring... probably 30k miles or so.