I am down to thinking it is a sticking regulator on the compressor. The regulator pictures show what appears to be a fair sized oil stain on the outlet side of the regulator suggesting there is oil residue in the regulator which may be causing the poppet valve in the regulator to stick shut. If you can get a small air compressor to use as a test, try plugging the hose to the Gravermach into it -- most small compressors are set up with a quick connect on the outlet so it should be an easy setup (noisy) for a test run.
