I was attempting to rebuild my MP GS3. I had it apart 2 weeks ago to install the vertical manometer. For whatever reason, even using the LM valve extractor, i CANNOT get the o-ring stack to come out. Has anyone else experienced that? In the meantime, I think it is possible the extractor scratched the inside of the stack...any advice?

Stephen, did you ever resolve your problem?

Are you using the LM factory tool? Is the little pin inside the collet (the part that expands inside the valve as you tighten the tool)? It seems that little piece, about half an (inch OK 10 mm!!) could have fallen out causing the tool to not expand properly.