Being the family fixit guy, I get to play with lots of interesting toys that are broken, have been "fixed" by someone else before or have became disassembled, etc.
Here are some pictures of a Marlin Camp 9MM I repaired recently for my Nephew.
It would shoot but not cycle properly.
I looked on the internet and everything indicated bad buffer - yes, sometimes the internet is a wonderful thing....
Replaced the non-existent original buffer with a new red urethane one and it shoots like a dream.
I almost feel guilty shooting it to test as it has extremely low shot count but that's the spoils of the repairman - I gotta test it and make sure it works!