Howdy JF2
The more I read about your problem the more convinced I am that you simply have a LEAK! Somewhere on that engine is a small trail of fluid! I think you should fill everything and park on a smooth dry place and run the thing in place for 30 or 40 minutes till you can see the fluid appear. I have never seen a head gasket leak that did not also leak compression back into the water jacket. You do not indicate that.
Your leak may be where you dread it the most.
Big Jim