Hey Umang,
You don't mention if it's a limited slip diff, makes a big difference but Penrite very popular!
With the C4 just Dextron lll, you can't get the original Dextron ll anymore! I used Shell Dextron lll even though I have a T5 manual transmission. Nulon are also good and they have a squeeze container for easy filling!
But I've found Penrite OK in my Diff and Engine.
Cheers Phil.