Valvoline says it on the back of the bottle (dura blend). Guess The other day when I looked at it I didn't see the small print.

 

Amsoil says that the additive MIGHT be needed. Had customers use Amsoil and others that it turned out it was always needed.They ended up with judder on turns.Try it without and see.All it takes is pouring a bottle in if the differential shudders.

 

If the bottle of gear oil doesn't say that the friction modifier is included, and your vehicle requires friction modifier (i.e. for a limited slip axle) then ADD IT. This is not complicated.

Rob

 

I used royal purple for LSD's in the rear, it has the additive pre-mixed. no issues