That's a Canton pan in disguise. I have seen a drip of
oil pretty common on the bolt head. It would not hurt to clean the rough surface (probably from their tapping). Careful not to get into the threads at all.
As Snakester pointed out you can get some fancy plugs that have a nicer grommet on them that usually take up the difference in the two surfaces.
Happy 500! Those are the tough ones.