Found one with the right number on the Speedograph site, so have ordered one (£120!!!!!).
In the meantime, saw on a TR site, where someone had replaced the flexi quill, with a solid one fashioned from an allen key which he ground square. He was providing them for other TR owners with good results.
So, armed with the old drive, I created my own and welded it up. So far it has survived the 25 mile trip to work. I've also re-routed the speedo cable - the original route had some quite tight bends, which may have been creating some friction. We'll see what happens....
