It will only push out oil at the front of the head coz that is where the high pressure oil feed passage is.
If the gasket was new and both surfaces (head an block) were cleaned properly then it would probably be a warped head.
Have to pull it off and check it with a straight edge and feeler gauges, or get a head shop to do it for you.
A cylinder head can be shaved and still be reusable. The amount shaved off the head before the head is stuffed, depends on the manufacturers specs. I know 18RG is only 40 thou.
Note that once you shave the head, it then increases compression slightly and will put more strain on the bottom end.