Interesting. This riveted boiler I have shows no evidence of ever being repaired or converted from solid screws to hollow screws. It was made just like any other hollow screw boiler except for the rivets, soft solder, and the inserted ceramic heater. It doesn’t have and never did have the soldered in bushings that solid screw boilers have. It seems more likely that to me that Tom Sr. was experimenting with the hollow screws before he started silver soldering the boilers and may have had a surplus of ceramic heaters to use up, which would account for the blanket heater designed firebox I have. Given Tom Sr’s track record for mixing early and late parts, this seems the most plausible explanation to me. I find it hard to believe that very many of these engines were sent back for repairs. I’m sure some were, but I think it would have been a pretty big expense to invest in something that was just considered a toy at the time. We will never know for sure.