Anyhow, with engine off
- wiggling the cables is fine, gear shift travels front-back and side-side
- wiggling the 2 arms that connect the cables into the box is less fine
- wiggle the front-back arm and the gear shift travels ok
- wiggle the side-side arm and the gear shift goes from detente to right, but won't go left
So I don't think it's the cables and I don't think it's the sugar cube (although I've not taken the cube out for a look - seen some far less than cubic ones while I've been trawling the internet for hints). I'm starting to dread the idea of looking for a replacement e153 box and then cancelling any fun for the next 3 years, to pay for it.
I am hoping that someone recognises the symptoms or has a better theoretical idea than I do, so I can start crying/saving or ideally rejoicing and fixing it up.