Steelslaver
I'm thinking that I've been wrong about some of my comments. Presumably the cylinder was opened by pushing the thumbpiece forward - otherwise it would still be in the frame. This means that the centerpin is free to move, maybe 3/16" or so.
Ralf - Is the above more/less correct ? Or, was the cylinder already open when you received the gun?
Steelslaver - If the pin will move forward and rearward, is it your thinking that you would pull the pin forward as much as possible, then cut off the pin at the top of the lower half of the extractor shaft, and then let it move backward, being pushed by the internal spring? That would give you a bit of space at the top end to mill as much as possible off the center pin, to get more space to work on the broken piece? If so, Ralf would not have to send the whole gun - just the bottom portion of the extractor, which is already out of the cylinder.
My thinking now is that this is what has to happen, one way or another - unless a very long Kroil soak might loosen up the broken piece.
Regards, Mike Priwer