Hi Blue,
Yes that issue with the cover plate is a real bugger as I've had a look at it all again this morning and I can't find a circlip that's accessible at all. The only place I think it could be is internally just like a drive shaft on a front wheel drive car which has a ring inside a groove that compresses when you place excessive lateral force on it thus releasing the nut assembly out of its housing.
How does that technology sound for a Villiers ?
Cheers,
BB