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I had the exact same problem. My brother and I took apart the regulator, found a tiiiiny piece of plastic stuck in the place where the rubber stopper should block the opening. After putting it back together it's worked perfectly ever since.
Thank you! I took it apart to look for a piece of rubber or whatever might be sticking. I pulled the little metal plunger and spring out, didn't find anything. But, when I put it back together, it worked again! Awesome! Thank you! You gave me the confidence to take it apart... Nothing to lose if it's otherwise broken, right?