Compression check won't isolate a gasket problem. It could just as easily be worn rings or a leaky valve. But! After reading the post about the fact that you have a full expansion tank and an empty radiator after a short trip it reminded me there was a comment back in October about exactly the same thing. Problem stemmed from a sticky check valve between the radiator and the tank. The fluid was all going out and never coming back in. Don't ask me the mechanics of it. Maybe the original poster will chime in and give details. I can't see where the check valve would be unless it's where the line goes into the tank.