Must have gotten a bad one. I bought mine back in 2012 and have not had any problem other than replacing a couple of the o-rings. Back then I got six caps and a connector for a little more than the cost of one of the original ball lock carbonator caps.
On the other side, one of my original ball lock carbonator caps developed a crack and no longer holds pressure. It still comes in handy for holding the disconnect open to draining all the liquid out of picnic tap lines before storing.
edit to add:
I also do the shake at 30PSI method, but disconnect before shaking. Paranoid about getting liquid in my gas line.