After looking at the instruction sheet (I've never built one of these I would still be inclined to think the fix is in the spring. If you have it going the right direction with the larger diameter end toward the tip, I'd try lengthening the spring a little. If that doesn't take care of it Replace the mechanism.
What I would do in the future is make a jig that would allow me to press the coupler/mechanism in without putting pressure directly on the mechanism....the mechanism is obviously not designed to be pressed in. It looks like a piece of wood with a hole big enough and deepe to pass the mechanism but rest against the shoulder of the coupler would work so the pressure goes to the shoulder of the coupler via the wood rather than the mechanism.
I believe that PSI needs to rethink the assembly and allow the coupler to be pressed in before the mechanism is installed. Every other kit I have seen that uses a screw in mechanism does that.
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