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If it's the same as mine just a long bolt through the back of the stock. Mine is slotted like a screw.
It may just be worn or bent.
Not a lot going on in there
It will be brutally obvious

Got one at home. Back in a couple of days and I can check it out.
It blocks the tripping levers from the trigger to the hammers from lifting.
Take the stock off and have a squiz.