Is it the rod getting stuck? If so, might add a drop of oil around the rod. I don't have a Clippard brand valve, but I've worked on plenty of solenoid valves in the past at work. There isn't much to them. As long as the coil isn't burned out, the spring tension isn't worn, and there is no interference for the pushrod to close the valve, then all should be fine. If the rod is starting to wear/damaged and it's dragging + the spring is worn out a bit from use, you could have that problem. If the spring is accessible, see if you can grab a similar tension/sized spring at the hardware store and replace. If the rod is sticking, lubricate it a little and work it by hand a bit until it frees up. If the rod is scratched/rough bad, then you might need to sand it with a Dremel to smooth out the rough surface, which 'may' be possible since it's CO2 and pretty rough on metals in the long term.
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