Sure is!
The FM is a LSD friction modifier and several other companies make it as a separate additive. It can actually be quite damaging to the seals too. I've been told it's only needed if you get diff chatter, but if I don't use OEM, I am thinking of using 4% to mimic OEM fluid.
For S65, we need 1.25L for diff and 2.5L for trans
