To do the pinion seal replacement on a rover type axle that uses
universal jointed prop shafts (Not the rubber doughnut type):

Assume the rear diff:
Remove the 4x 9/16" (14mm) bolts that hold the rear of the rear prop shaft and tie the prop up and away.
Remove the large nut on the diff flange:
Either use an impact socket driver
Or
Take a flat steel bar of about 5mm thick and 500mm long, drill a 10mm hole about 10mm from the side near the end.
Fit a socket to the flange bolt and bolt the flat bar to the prop flange with one prop shaft bolt such that if you turn the bolt in the anti-clockwise direction the flat bar will push up against
a) the bolt in the hole and
b) the socket and
c) the ground/suspension/body
 

Now you can loosen the bolt. Some bolts have a split pin through them, this must be removed before removing the bolt.
With the bolt out, pull the flange out, then , either use a large spanner (like 35mm or so) or a large screw driver and lever the old oil seal out. (Do not hammer it in between the seal and the diff casing as
you will mess up the sealing surface.)
With the old seal out check it against the new one (if it is not mangled
too much !)

The replacement seal will be rubbery all round, lightly oil the outside of the seal as well as the inside lip, then oil the diff housing a bit.
The seal can be tapped into place CAREFULLY while always keeping it parallel with the diff opening, this is done better is you use an old bearing shell or a piece of tubing with a diameter slightly less then the outside of the seal. (Slightly like 1 mm or so)
You can tap the seal all the way home, as it will sit up against a shoulder - do not hit it hard - it should go in reasonably easily with a regular ball-pein hammer.

Oil the diff flange inner seal and push it on gently - rotate it a bit
as it goes on ( jack up a wheel to do this) to make sure it does not
grab and bend the lip.

Fit the bolt with a bit of locktite and tighten it very tight ( Same
procedure as for loosening)
Refit the prop shaft and off you go.
Depending on the level of the oil in the diff - it may run out when
changing the seal - always check the level after an oil seal change.