Buy some ultra black RTV, run a fairly large bead on the diff cover, put diff cover on and hand tighten down with a couple bolts. Let it sit like this for a while, maybe 30 min. Then fully tighten everything down to proper torque. Wait at LEAST an hour before filling up with fluid. Overnight would be absolute best. Just make sure when you go to fill it up the RTV is at least rubbery. If some squirts out the edges you can touch it to make sure.