Well, I got a 2w capacitor at the weekend - another 26p spent!
I've stripped it down again, and it still doesn't work - or rather it is exactly the same - you can get manual mode, but only if you press down on the mode dial.
This is where the flexible PCB plugs in to the camera. I hoped it might be this that was loose, but it would seem not. It works exactly as JeffJS says - you slide out the black plastic part and the cable just comes out. The bunch of wires above that are the ones I don't want to unsolder, and it is two of those you need to short out with the resistor to discharge the capacitor for the flash. You can see some of the weather sealing too.
The second picture shows the contacts -on the right is the bottom of the mode dial, and on the left is the flexible PCB is contacts. The plastic holder with the PCB attached screws on to this (screw holes at 11 o'clock and 5 o'clock around the bottom of the mode dial).
The outer metal contacts are for the metering mode, and the inner ones are for the mode. I have bent one of the sprung pins on the metering mode, but that doesn't matter as they are in pairs and only one of each pair is needed.
If you disassemble the dial further by removing the centre screw it is just the plastic dial and a tiny ball bearing on a spring (so it stops in each mode position) - nothing electrical, so that cannot be the problem.
I don't think there is a problem with the connector in the first picture, which just leaves the contact between the flexible PCB and the pins - but I can't see a problem there either - bit the fact that it works when you press down on the mode dial suggests the issue is one to do with something not connecting properly somewhere!
There doesn't seem to be any damage to the PCB as far as I can tell - apologies for the rubbish quality of the pictures, they are from my phone.
Any ideas of what to try next much appreciated!