I was gonna replace the pinion seal on my diff, but found out the staked nut on pinion would need to come off and then outer housing off, the seal out, new seal on, put back together. Don't think shafts had to come out.
BUT
the staked nut needs to be torqued back on and the lash of the diff cheacked. I realised the diff was too cacti to bother (you could load the diff by the lash, like let clutch out little, feel the lash take up, then the wheels slowly turn), so I swapped the diff over when i got my new shell.
Find someone with an Haynes America AE86 Manual and photocopy. It has all the info. Tho a TA22 book or anything with the same era diff will have the same info.