What kind of gear oil for 8 3/4? Why not synthetic gear oil?

First of all, synthetics and friction modifiers do work well together, Chrysler does it. I did it in my dually Dana 80 tow vehicle with out complications.

Secondly the type of differential he has doesn't need a friction modifier anyway.

why wouldn't he need one? i was taught that all limited slips need a friction modifier. my previous info was straight from a tech at richmond gears.