The seals are behind the "press to fit" bearings on the axle. To replace the seal the axle bearings have to be cut off or pressed off the axle, which destroys them. This is done by a machine shop, not in your garage.
On the outer mose edge of the axle is a four bolt plate, may or may not have a "gasket". THAT plate is what holds the seal and bearing in place. The plaste gasket (if any) is just to keep dust and dirt OUT, not
oil in! The "seal" holds the
oil in. Afer the seal comes the bearing itself. After that there is a press fit retaining ring snugged up against the inner bearing race.
Cut the retainer with a chisel and hammer but good luck doing that to the bearing itself! Aint gonna happen!
Ernie
Edit: This of course assumes you really DO have a 9". the "removable" carrier or center section type rear end. The 8" is totally different and the seals can easily be replaced as they go in the housing, NOT on the axle.