Bolt Failure at Extractor 1937 S/42

[sdmark777]

I have a well used WWII, S/42, 1937, 9mm Mauser Luger. This is all matching and original. Both sides of the trigger are dented in slightly. But the main issue with this Luger is a failure at the top of the bolt where metal has sheared away on both sides of the extractor. The extractor is in perfect shape and original to this Luger. There are what I would describe as wings on the left and right sides of the extractor, not visible without disassembly. These wings limit how far up the extractor will rise. It appears these wings pushed up against the bolt and sheared off small pieces on each side. This was the condition this Luger was found in many years ago.This Luger shoots fine, and is the only one of my Lugers I will shoot. I am looking for the following info from you folks.

1. How common is this bolt failure? This is the only one I have seen like this.
2. What do you all think the cause is? Poor metallurgy? Poor hardening? Excessive pressure from hot rounds? Milling dimensions too tight on the extractor cut out? Or something else?
3. If you have seen this in other Lugers, I am curious as to which ones? ie just WWII?, just Mauser?, WWI?, Commercials?
4. Also curious about dents on back of trigger on both sides. Anyone seen that kind of damage. Is it from dropping the trigger when disassembled?

Thanks for your thoughts and information. Mark