I just changed out my two front bearing assy.s with Timkins. I also had the rear end done.

I was told that the rear bearings are like the front, in that they are "pre-oiled" and don't take grease packing, or they are internally packed from the factory. Is that true?

Also, I have to ask what purpose the front O-ring does when the whole interior face of the assy. is exposed anyway. On my '95 S-10 when I changed out my dust plate and had to remove the assy. it seemed like it was enclosed with a ton of grease in behind the assy, but on the 2000 Blazer, the hub and shaft are wide open. So what would the O-ring be sealing?