Compression testing will show a change if the gasket is violated.
Regardless, if the compression ring isn't damaged and it's leaking via the oil passage, you'll still have to yank the head to repair the leak. I'm guessing the compression ring is leaking because the oil passages have dowels in them. As well, no pressure to push anything out, unless a pressure source is created.
“When the going gets weird, the weird turn professional....” ~ Hunter S. Thompson~
R.I.P. Rubberdown. 1971-2012