Hi Mark,
Firstly welcome.
I'm just going over my Dax on return from paint and have just been looking at the handbrake pads.
Assuming you have a standard chassis (not a De Dijon) you have in board brakes with seperate handbrake pads. The Jaguar manual says they should never need replacing !!
And it does look like they are impossible to get to. With the car up high enough, the wheels off and some small dextrous hands it might just be possible to replace them in situ. I've just adjusted them in that position. It would help also if you have access to the top of the rear axle from inside the car.
However it would a lot easier to remove the rear axle which would also let you get a better look at the diff.
As for diff oil, that depends on what diff you have, the Powerloc diffs require Limited Slip oil usually labelled as LS
Other wise it's normal diff oil I believe.
The diff should have one or two aluminium tags one tag giving the gear ratio 3.54 for example the saying PL if it is as a limited slip diff. Filling up is simply a matter of putting oil in until it starts to exit the filler hole. If oil is leaking badly the diff may need to be remanufactured or replaced, which means removing the rear axle at which time you can easily replac the hand brake pads.
I'll see if I've got some pictures and post them later.
Andi.