I highly recommend that you also replace the O-ring and gasket at the mounting point for the oil cooler lines (where the oil filter attaches).
Felpro has a gasket set ES72671 that includes all of the gaskets, O-rings, and seals for the oil cooler lines. Or at least make sure the new lines come with all the gaskets, O-rings and seals.
I had an oil leak that I thought was the rear main but actually was the O-ring for the oil filter adapter.
//2000CAYukon