Can be done in situ.

Pics from a 2wd saph but still the same.

Unbolt the drive shaft on the side you want to change.



Remove the rear diff cover (get something to catch the oil in when you take it off)

The stub axle has a circlip holding it in the diff. You can just make it out in this pic.



Pull that off and you should be able to pull the stub axle out of the diff.



Seal pic.



Remove old seal

Fit new seal.
Fit everything back together (use some sealant when refitting the diff cover)

These pics are from when i stripped/rebuilt my diff. When you get the rear cover out take a look at the gears inside. Mine didnt whine or anything but the teeth on the gears were chipped and very worn!

Mart