You also need to lightly grease the outdrive shafts before you stick them back through the diff housing. fill the diff about 85% of the way full with oil and work the gears back and forth a few times and let the oil settle. I usually top off with oil to the top of the planetary gears, then new gasket and screw them back together in a crossing pattern a little at a time until tight. Then i usually mark what oil I used on the diif case with a sharpie paint pen, or you can lightly scratch it in.