Common issue, I'm sorry I forgot to mention it. The screws get loose on the resistor, and it presents a high resistance that indicates to the RCMC that there's a smoke element failure. One of the first things I check when I open a smoke unit.
I can only take solace in the fact that the Lionel tech didn't think to mention this obvious failure either, we both whiffed on this one.
One oddity that I still don't quite understand. Why did the new smoke unit still indicate the same failure? I'd have thought that one would have the screws tight.