Yeah, it's the same deal with the ribbon cables - just tinned wires straight into the connector. Good to have someone confirm that they could be a prime suspect.
I don't have any contact cleaner right now, so after I'd pulled a couple of ribbon cables out and re-seated them (just a couple from the master board to the boards carrying the output connectors) I decided to button it back up again until I have time to give every connector, pot and fader a good going over with Deoxit. The board is needed this week for the band duties that it's been performing reliably for years, rehearsal on Thursday and a Saturday gig, so I didn't want to introduce more problems before then.
I only found out that the right channel was out when I was demoing it...I run both mains in mono for my own band, from the mono output as well - so I haven't tried using the stereo outs for years. We've got a bit of a break after that until the next gig on 15th Nov, so I'll get some contact cleaner and give it a good go over on Sunday.
If it fixes it and it sells, that'll be great, if not I'll probably pull the trigger on the Presonus by then anyway.
Thanks for your help
Rickenbacker 4001 > Zoom B3 > ART Pro Channel> Crown XLS1000 > Barefaced Big One