I would expect a vacuum leak would show up also if the intake gasket was pulling oil in. If it is from ring seal it will be showing up on you spark plugs pretty quickly.
Cometic makes a compressible fiber gasket that is a little thicker than stock for irregular surfaces.
https://www.cometic.com/products/C5778-060
I have noticed the gas we have here in the Midwest can leave a brownish red resin in the intake ports that resemble’s oil. Not sure what exactly is in the gas that causes it, may from the MTBE used in our fuel here. The left over resin really shows up if it runs running rich.