Many thanks for both responses and apologies for my tardy acknowledgement.
When I said ¨lens¨, kamkart1, I meant the same as Innovv did when they sold it i.e. the lens with cable attached but the link you gave is interesting and I've saved it for later.
What made me believe some damage had occurred was that recorded images were completely out of focus and kensteele's reply encouraged me to dismantle the housing containing the lens to see what was what. After all, not finding any source for a replacement new or secondhand, I'd nothing to lose.
The lens is screwed into a rectangular body containing the light-transforming wizadry and, after focusing, is held in position by a gnurled locking ring: except it doesn't appear to lock the lens from turning, and changing the focus, when screwing on the aluminium body. There appears to be an insert in this body which is a tight fit around the lens and each time I re-assembled it, the lens got turned from where I'd set it in focus. It would appear a special tool (or knack with an ordinary one) is needed to remove this insert and fit this over the lens before screwing on the outer body. I hope to get time to try this at the weekend.
I'll let you know what happens.