That is a known hot spot for the magneto plug especially on the boats for some reason. It gets so hot there that it cooks the wire and then it gets brittle and the sheathing breaks apart. My theory is that the wire crimp on those 3 terminals is not good and adding resistance which heats it up. My solution was to soldier the crimp area after I put new terminals on. I tested it and it didn't get hot but haven't heard back from the boat owner so not completely sure if that solved it.