UPDATE :
Dug this back out of the cupboard today and wish I hadn't , stripped it right down today and the thing pretty much fell apart

odd bits of metal fell out when I took the internals out , god knows where they came from

.
I think I will leave this one as it's simply worn out

and sourcing parts may be more hassle than it's worth , shame as I would have liked to get it to atleasts fire something . Glad it didn't fire as it looks bloomin dangerous !!!
Was worth a try though .
Dave