I'm having my rear end gone though and redone along with the Trac-loc. Since the clutch packs have to sit in the friction modifier before they install them. Once it's all said and done for me to come pick it up from the shop, I'll need to add fluid to it once I get it installed back in the car. Am I going to have to add more friction modifier when I fill up the differential and what kind of gear lube would you recommend for filling it up???? 80w-90?