Are either of the seating surfaces worn? If they're not flat, it would take a good bit of squish for it not to leak. I just tighten it snug so its not leaking and call it good. Given that the threads in the head can be delicate, I go easy on it.

This shall pass, be still and know.
2006 XT225, UNI filter, ProTaper bars, MSR handguards, SS front brake line, Shinko 241's.