Thank you to you helpful persons. I bit the bullet and used the mole-grips with some lead strip (protecting the thread) to get the nut/boss off. Then used the tool makers clamp compressing the parts as shown to put the dial back together.
Cheers fellow metal manglers!
Mike
PS apologies for mis-spellings, etc in the original post – that would have been ‘must do better’ from my old English teacher! I was a little peeved.
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