Okay, so my sm5k worked fine and for some reason it quit firing. I opened it up to see what the problem was and I found that the notch on the end of the valve pin has been worn down, I found the o-ring over the notch because of this, therefore the gun won't fire. All the other parts are in great condition, but without that, it can't do anything. Any ideas on how I might be able to fix this?