Wanting to change oil for thicker stuff in the diff unit itself, How do you do this. Kev.

the lsd part of the diff is not filled with oil,its a sort of super sticky grease,you can change the oil as normal ,if you want to check the lsd you have to unbolt the rear case flick the shaft flange clips out ,pull drive flanges out and wind out the bearing carriers .then pull out the full diff and unbolt in half be carefull with the plates keep them in order,all this will disturb your preload so probab best left to someone who has done a few if not confident....

Silicone grease/oil I believe. But as far as grade?

this man ended up rebuilding the viscous bit by accident: linky
not sure where he got the silicone stuff, but you could ask him