Niksan Niksan Ozark W

Oh, you shot it out the barrel when it broke. That O-ring slides back and forth under the transfer port I do believe. Just need one that fits snug. My spares bag had one. However, I'm on my third one. I got it from an O-ring kit from Amazon. Seems to be working just fine. If I could remember which one I used I'd tell you the size right now. Otherwise, I'd have to tear mine down.
 
Well, then thats the problem....I dont have one in that groove at all. Nor is there a spare in the kit....like you have lots of o-rings. I put an o-ring on the stem and see how it goes. Thanks again.
I just pulled my parts bag, and I tossed the broken one in there to save for reference. It's a 1x5mm. A 1x4mm will work as well.