Hmm, well. I made "progress". As expected the WD 40 did nothing. I'm not convinced having the bolt loose would be of any benefit. I found a cheap, battery powered vibrating multi-tool in my barn and used that to remove the aluminum fans and get the rusty bolt down to a nubbin. But considering where the nut is, hidden in the ash tray cover or in the concave bottom of the grill, using a hack-saw isn't possible.
I can see now why google mentions the Dremel.
Before I ruin it, am going to spend some time and see if I can find a Dremel or something similar. I'm on it!
xo, Biggles