You can use M1 LS in the rear diff, but do not run it in the tranny. It has limited slip additives (hence the LS) and usually makes the synchros too slippery. The synchros need a bit of friction for the best engagement and that's the point of the cocktail. If you want to run Mobil synthetic, try Mobil Delvac. It's tough to find but I get mine from lufteknic. Delvac does not have Limited Slip additives.