Which oil for differential you use ?
My service manual book told use shell spirax super 90 or for top up EP 90.
As I understood , I can use any brand mineral oil with 80w-90 as alternative for shell spirax super 90 ?
Somebody used synthetic oil 75w-140 instead mineral 80w-90 ?

 

Opinions are all over the board on this, as with engine oil.

I use whatever name brand is on sale that day, 80/90 weight. Shell, Valvoline, whatever.

Some are already formulated for limited slip differentials and are labeled as such. If not, you'll need an additive. Auto parts stores sell the additive. Or use GM part number 1052358

Cheers
DD