4. Once the cover was reinstalled, I fed in almost two bottles of the Royal Purple Max-Gear 75-90. Max-Gear is designed to provide protection to heavily loaded gears with a blend of synthetic oils and Royal Purple's proprietary Synslide additive. All viscosities of Max-Gear are formulated with hypoid friction modifiers, which are necessary for use in clutch- or cone-type differentials. So, if you have a posi, no additional additives will be necessary.