I have gone through 2 of these (back when they were discwasher) and still have one, and I think yes one went bad and no longer had any resistance to the pull of the lever and did not "hiss". You should be pulling the lever very slowly, with as few "clicks" as possible, pulling it quickly produces many "clicks".
Is my ZeroStat Gun Toast ?
I bought one of those Milty Zerostat guns some time ago, and it used to click 2 or 3 times whenever I pulled the trigger and again when I released it. The clicking noises suddenly stopped cold turkey - is my gun now useless ? I suspect that it is, but informed opinions would be welcomed. thanks