good news, mostly.

Firstly, new keyboard strips fitted, working fine.

Secondly. video output fixed. Whilst I can't see a visible break, the pcb track feeding the output connector centre pin was totally open circuit, so a quick bridge with a short piece of wire has done the trick.

Thirdly, the 5" monitor that I got locally either shows a 2/3 size version of the full display, when the 3k is told to feed a PAL signal, or full width chopped slightly at the bottom if I feed NTSC. I think I'll be running the latter for a bit because...

Fourthly, having now disassembled the LCD module completely I'm certain the fault is in final bit of PCB that connects to the lcd module itself. Can't do a thing about it, in fact based on it's behavior whilst I was re-assembling I think it's going to get worse.

I'll investigate the external monitor situation further. The 5" thing I have is merely adequate. Something a bit bigger is needed but I'd also like more control over the video scaling - the current thing has no control over scaling.

Thanks again to you all for your help here!