Thought I'd investigate after feeling/hearing a crack on full lock, and concentric travel of the steering wheel on the way home. Seems the boss cage has failed. As luck would have it, I came across a replacement wheel with boss on the Internet, so that should be with me by the weekend.
After a chat with Mr Foxon of G.E.E, it seems this was a regular fix under warranty so not so bad after about 20 years and 95k miles I guess.

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"DOT" 35th Anniversary Edition Plus 8- family owned from new. Rolls Royce Pewter.
06 Saab 93