Do not use sealer on composite head gaskets. Steel or copper shim gaskets, yes, but not on a layered type. If the holes are blocked, there's probably a good reason. One of my students opened up some head gasket holes in a small block Ford V8 that he thought the factory "forgot" and ended up with an instant overheat. It turns out the gasket was made to work interchangeably from one cylinder bank to the other by observing the "top" marking, and the holes in the front of the head were supposed to be blocked so coolant would flow toward the rear of the engine. Don't second-guess the people who make the gaskets.
Jerry
