I replaced one on a friends very old 500. It belonged to his father and had a lot of sentimental value so it was old and beat up, but I wanted to take care of it.
Replacing it was no problem, getting it apart was. The piece on the inside had come apart and acted as a perfect wedge for the action and it was locked up tight. I spent quite a few hours trying to get that thing apart. I finally did and everything‘s OK but it was a real booger.
On a sidenote that Action was just dry as a bone. When I give it back to my buddy, I told him that there is this new thing out there. It really helps mechanical things of any type function. I had him really going he asked “what is it?” I told him “It’s called oil” we both had a good laugh.