I know it's not what you want to hear, but I'd peen the pin a little and take some sandpaper to it and smooth it out. Hopefully you'd be able to tighten it up enough that it won't move any more. GEC should have taken care of this for you, and I'm not trying to dismiss that this should never have happened in the first place. I'm just trying to offer a solution so that you can get back to enjoying your knife. Good luck, and post some pictures if you are able.