The seal really dosen't support anything, it just keeps the gear fluid in the diff. case.
When you go to change the seal, you must put the pinion nut on in EXACTLY the same position as you took it off. If you get the nut on in a different position, it will mess up your rear axle in a hurry. Mark the pinion nut relation to the driveshat yolk, and the driveshaft yolk to the rear axle.
It would also be a good idea to take off the cover and change your gear oil too, as well as inspect the innards to make sure they appear to be in good shape.
Good luck
