axle seal?

I'm looking for the correct part and terminology that goes along with it. I've looked at page 40 in the online catalog over and over and can't find what i'm looking for. I need the seal that keeps the gear oil in the differential, specificly in the rear. This bad seal is allowing gear oil to drain out the end of the axle tube when i park on a slope and has now caused bearing failure. Bearing are less than 1000 miles old! What am i looking for? Where do I find it? And is it the same for front and rear?

Thanks for any help.
mw

forgot to add. i'm working on my 91 swb rrc with abs.