rear axle seal.. leaking gear oil

[firstclass]

Yesterday I added some gear oil to my differential (2wd 1984) which has been leaking from the pinion oil seal. I'll be replacing that seal as soon as it comes in.
In the mean time, I needed to drive the van probably 20 miles or so, and I noticed this morning that my left rear wheel is leaking a lot of oil at the axle. Probably more noticeable because of the oil top-off.
Do I need to replace both my axle oil seal and the retaining gasket? Anyone have experience with this job?
Should I go ahead and buy/install new wheel bearings?
Thanks for the insights