The sensors should have a thread sealer on them, either teflon tape or a liquid pipe sealer with teflon. Most of the gaskets do not reqiure additional sealant on them, except in the corcers of the intake and oil pan, where the seams of the timing cover meet the block, and where the rear main cap meets it, just in the corners. You can use a wet silicone spray or some silicone grease for the injector "o" rings.