I never seen a 45 that looked like that. The first thought is were they all burning corn? Second is I live in corn country here and never seen anything like that. But all corn is not the same as there is different minerals etc in the ground and the residue could cause more damage to the metal. I remember a factory rep from Harman came though the area with a trailer with different models of their stoves and we could ask them questions about their product. At the time I was more concerned about the rapid buildup of hard material on the stirrer and what could be done about that. His answer was to have a extra stirrer and when one got round pull it out and put the extra one in. Then put the first one in a pail of water as the hard stuff will dissolve. Or you could burn a mix of corn and pellets. I wonder if the stirrer got so worn out it warped from the heat and started rubbing ? How old were these stoves? The one picture looks shiny as something has been rubbing which made me think the stirrer rod got bent from the heat and was rubbing.