Using the mash hammer and chisel wedge it between the diff cup and hit it so it pops out. There's a retaining clip inside which you need to free up and the only way to do it is to pop the cup out:
You'll now see this:
Which is the seal you need to replace. On this side you can remove the plate held in by the three bolts you can see then using some tubing 'press' it out in a vice. Alternatively you can tap a screwdriver in down the side then force it out, which is what you have to do on the other side. Be careful not to mark the alloy as it's not very strong, be gentle but forceful enough to get the seal out! :
The two seals ARE different so make sure you have the right one:
To put it back in you can either press it in with a vice or get the tubing and tap it into place using the mash hammer. Make sure you clean it all up before putting the seal back in and make sure it's all the way in!
Note : You want tubing around 6" long to tap the seals back in, the piece used is just as an example. If you use tubing make sure it's a square cut and there are no sharp edges. The seal in the pic is also ****ed as it's an old one
Repeat for the other side. You have no choice but to force a screwdriver in as the plate is not removable and is fixed in place.
Clean the diff cup.
Pop it back in place, making sure it's 'locked' onto the splines.
Using a rubber mallet hit the cup till it goes all the way in, pull it to make sure it's in properly.
Put a healthy amount of CV grease in the cup.
Clean up the CV boot and cup then put the boot over it and cable tie in place.