On 07/06/2021 18:47, Murmansk wrote:

Have you cross threaded it putting it in?
--
bert

No danger of having cross threaded it as it's never been taken out - it just goes up and down through the nut which is welded to the mechanism.

Anyway, a call to Witter revealed that I can get a replacement bolt and the associated nut and its metal support for £15 including postage so I've ordered one.

Buying stuff, PTOI
This is D-I-Y. Mine some ore, smelt it , cast it into ingots bite ;
support, nut and bolt shapes with your teeth...
voila a replacement nut, support and bolt.
FTAOD ;O)