OP signature indicates 5/73 build. If he's got the original F engine, there's no plug, but the original copper tube.
Pretty sure. I torqued it to spec and sealed it really well when I installed it. But it's probably worth some further investigation.Should be an o-ring on the shaft. Are you sure that it's not coming from the tin pushrod gallery cover (commonly called the "side cover") behind the distributor?