Thanks. These head gasket questions come up all the time, it will interesting to see what Cometic comes back with. If you stick a wire through those holes in the head you might find that they're connected, so blocking one does just change the flow in that area of the head, but not stop it. But that's where flow is low, the back of the head, from what I've seen on this forum so blocking a passage there seems odd. Maybe they know something special.