Sell the bass? Definitely an option as I have some very nice instruments including a Fender CS 64 Jazz that has a very comfortable neck and curiously wider than the Elrick at the 12th fret (58mm v 55mm) but slimmer at the nut by 4mm. Also a recently purchased new Overwater Progress 3 that has a great neck and slimmer than the Elrick all the way up the neck.
Contact the manufacturer? I once tried to make contact with Rob Elrick but got a very curt response, so I wouldn't think I'd get much joy there. The official spec for the bass gave a nut width of 40mm but when I measure it it's 43mm.
A luthier? I have a luthier who lives not too far away and does all my repairs and mods. I've spoken to him and he reckons he could do it but I thinking about the points you made previously about dot positions etc. The other thing is that I would probably lose the MOP side markers. But thinking about it, he could probably make me a new neck to my spec and, that way, I would still have the original if I wanted to sell the bass later.
Your thoughts are much appreciated and I'm very grateful for them.
Kind regards
Pete