Permatex Form-A-Gasket.

They make 2 kinds, one that sets up hard and one that doesn't so use the one that fully dries. Clean the heck out of the openings and then wipe a little sealer in the hole and drive the plug home.

Lots of people stick these in dry and never have an issue. My experience is if one does leak it's always the toughest one to get to.