So, have got the LCD out and... the only mildly suspicious cable is the ribbon cable that goes across the back and loops round into a ribbon cable edge connector. So I loosened the clamp, waggled it a bit, replaced, re-assembled the thing,and the LCD is now OK. Still goes dodgy if I press top right so I suspect I've actually made no real difference!

I'll see how this goes in the next few weeks.

Thanks again for the help.