I have changed out a few large copeland discus compressors in the past couple months. i have been having some trouble getting the new gaskets to seal(the green paper ones). They dont leak bad, just a little white foam when I check with bubble spray. I made sure to clean the surface of both the compressor and the valve where the gasket goes. And I made sure I bolted it on snug. Am I doing something wrong? Any tricks Of the trade I need to know?