+1 on the rtv, but make sure it's ultra grey. It's factory sealant for a lot of manufacturers and great stuff. Also make sure everything is clean and dry. Use brake clean on a shop towel to wipe down both surfaces before application. This is not a situation where if a little is good, more is better. You don't want it squirting out inside, breaking loose when it hardens and then blocking off the oil screen. Also, tightening from the inside out doesn't apply to gaskets such as oil pan, valve cover, etc.... You tighten them in a cris-cross pattern a little at a time (in steps) until tight. This keeps even pressure on the gasket and keeps it from kinking or slipping out. Whenever possible, I try to give the ultra grey 24 hours to cure before adding oil and running it. Guaranteed seal, but it can be applied and ran right after. It's common practice at repair shops.