The cover itself wont leak.
If you do it yourself just make sure to clean the gasket surface on the rear differential very good, I usually use a die grinder with a light grit wizzy wheel, then emory cloth, brake clean the ring and spiders, wiper it all clean, brake clean gasket surface 1 more time, apply gasket sealer to cover and stick it on, put all bolts in by hand and tighten in a star pattern.
torque is probably around 15 ft lbs, its easy to strip the threads in the differential, 1 bolt stripped can cause it to leak.
Ya, I was more concerned with the drain plug leaking... not so much the cover.
I was reading on the jeep forum a guy had a problem with it leaking....