Dan,
You could try getting a set of those valve covers with a breather hole in them and then use the breather caps and see if that helps. Also as XB-60 said, you may have a very small
oil leak that burns away before you can see where it is. I used some stuff in my
oil once that a black light made visible and found that I had a very small leak from one of the valve covers but it was not enough for me to see as the heat burned it away before I could find it. The black light showed where it was and I changed the gasket and that stopped all of the smell and leak.
Ron