Positrak gear oil


Need to change the differential oil--clutches are grabbing as I go around turns . I am considering Royal Purple or Red Line or something else. Looking for recomendations. Are all the rear end gaskets the same for '85 posi?
i used mobil 1 synth gear oil and a bottle of GM posi lube.. works for me, my diff doesnt leak AND when we checked the fluid, it was still clear and brand new looking after over a year.. neat huh
Use the GM posi additive and no gasket, just silicone. Silicone won't leak and cars are starting to come that way from the factory. All the 8.5" 10 bolts use the same gasket whether they're posi or not.