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if you do not wish to spent the time - take Gypsum Screw (Drywall Screw) like
place the tip of this screw in to the center of pinhole, and make some light hits on the screw (by wooden handle of screwdriver or something like it). Or just press on the screw and shake it a little.
I did it with my HP hose, when small hole on it was stuck.
Such screws has very sharp tip and hardened steel, and it can help to make small hole.
A slow reacting SPG is symptomatic of water infiltration through the orfice which is likely already into the bourdon tube. I would toss it and get a new. I was diving with a guy who ran out of air because his needle stuck at 1000psi or so.
I thought of the airline being an issue as a well, it got the same cleaning as the gauge. Then I swapped gauges between my other lines. All 3 gauges sweep to the same levels and at the same approximate speed. I used 2 tanks at different pressures, both are below 800 psi, I need to fill... I'll check them full once they are filled.
It will get permanent decommission if it acts twitchy.
I've lost track of dangerous hobbies I've had. The correct thought process is what will I do WHEN my equipment fails, not IF it fails.
Sounds like you're just blowing liquid deeper into the bourdon tube.