750 rounds is of no consequence whatever to a Parker Repro. I've fired thousands and thousands in my 20.
You may have a problem in your right ejector mechanism. I don't know how to explain it but I had a problem in my ejector mechanism in the forend and the spring mechanism to fire the gun was working against the spring mechanism in the forend ejector causing misfires and lack of ejection as well.
Who did you take the gun to in the Boston area? I live in the Boston area - maybe I can recommend someone.
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