most synthetics don't need friction modifier. put the 75/140 in there and go make a tight turn, if the rear tires chirp then add a little at a time. I've never added friction modifier with the redline gear oil i use
Running the Mobil 75/140 LS in mine that already has the modifier in it. Seems to work the same as the factory fluid+modifier specs when it comes to pulling 2 tires.