Oil pooling

moper said
It's an old SE trick to use a thin film of grease so the gaskets release and can be reused. I've done it before too - with cork gaskets.

That's exactly what I do, just a thin film of grease on the head side of the gasket (cork) and when you pull the cover, no sticky. :D

OP, what valve covers are you using?

Are they possibly hitting the intake and not seating properly?