The additive is a friction modifier, check at an auto parts store. It may be sold as a limited slip additive or supplement. When I ran a clutch pack limited slip in my Jeep I used Stay Lube Equa-Torque limited slip additive. When I worked at a GM dealership they too sold their own additive under part number 1052358 Lubricant additive, I'm sure by now that number has long been superseded.
