Thanks for the replies Brian and Jim.
I live near Selby in North Yorks.
I may have found a repair method using low temp aluminium/cast/monkey metal welding rods. I've ordered one and there looks like there's enough metal to get a good key, so may work. Not a huge lot of stress where it is, and I can pre stress it before I do the repair. If not a new unit from the states. $15 for the unit, $45 postage (ouch)
Oh well, paid next to nothing for the lathe itself, so I've learnt a lesson, these units can be fragile. I could always split it and sell it for spares to fund a more modern unit if I have to.