Hi guys. Greetings from down under after a bit of an absence.
Not knowing the service history of my ‘74 4/4 four seater I thought I should perhaps replace the diff oil.

There is a drain plug underneath, a filler/level plug on the side at rear and what appears to be a filler on the top to which a previous owner has fitted a ? filler pipe with what looks like a grease type nipple on the end ( not sure why )

Would this be a Salisbury diff and if so what oil should go in there? Top up or completely drain and replace?

Thanks for any help, Neil.

1975 4/4 4 seater, cream over blue; Q3 Quattro; Bicycle; Walking poles.