I have a Remington Sportsman 58 I took to the range today where it jammed after one shot. I got it from my dad and it hasn't been fired in many years. When I got home and took it apart, I found a loose plastic piece inside that appears to fit into a hole in the rear of the receiver right behind the breech bolt. The receiver is a mess inside and I will clean it thoroughly, but my question is about the plastic piece. It doesn't appear in any diagram or parts list I found online. Is this part necessary? Does it protect the bolt from contacting the receiver? Should I tap it back into the hole and hope for the best? Any advice would be greatly appreciated.