Great, I now have driver's side windscreen wiper.
Despite the fact that the old one was slipping on the spindle, I could not release the grub screw!
I ended up taking my small angle grinder to it -- (after protecting the windscreen, of course).
Once I had the old one off, fitting the new one was very easy!
Not used it yet. I plan to cut it down to fit an MGB/MGC wiper spindle as a replacement for the worn on. I am sure that there is a market for replacement spindles for the MGB/MGC.