Not really, but I'm closer. When I first installed the new regulator, the bubble counter ran like a champ for a few, then petered out to where it had been. SO I know that a pressure surge will get it moving. I have a new check valve I'll replace the old one with before I try anything else, but that's going to involve boiling water to soften the (rather old) CO2 tubing attached to the bubble counter. I've had a lot on my plate this last few weeks, I'd have usually gotten to it by now but the tanks are doing well so I can move it down the list. If replacing the check valve doesn't work, I'll order a new needle valve. If that doesn't work, I'll replace all of the tubing at which point literally everything will be new.
Nothing good happens fast in an ecosystem.