Well, I hate to be the bearer of bad news, but a lot of 51s that were shot a lot developed issues. I was selling guns back then and they fell out of favor fast. The Ithaca Mag 10s broke parts, and I fixed a lot of those, but I can only remember working on one 51, and I don't remember a thing about it. Some of the Ithaca SKBs were pretty fair guns, but I think they peaked with the 37.
What could have happened... did.