Hi all. Changing gaskets and noticed my no. 6 cylinder (area on head) was tapped clean thru to combustion chamber and tapped off (top) with a pipe plug. Thought little of it, till checked my "parts head" and noticed same. Was this a tap for compressed air or something? Also- I know modern books say do not reuse copper clad asbestos head gaskets. Also know reuse was done before in the millions of tractors and cars built with these gaskets. Anybody have first hand experiance with reuse success/ failure/ sealers (I like brush on non harding stuff) etc.??? Thanks!