Thank you Pinballdave and Clan for your information.
Pinballdave, to answer your questions, I've owned the car since 2014. However it came with loads of receipts that show that not only was it seemingly well looked after, but it did indeed come with its fair share of problems noted in the service book or other documentation.
I'm the one that cleaned the CEM and ECU contacts last year and yes, back then the CEM did indeed have some evidence of green corrosion on some of the pins. This time (today) I removed the CEM again and stripped it right back to the circuit board for a cleaning where as last time I cleaned it in it's plastic case. Some of the pins were indeed showing evidence of tarnish so I cleaned them up and put it all back together. I have not applied any dielectric grease as yet but I plan to get some and apply it asap.
Where can I get download VIDA from? It sounds like it could be a handy tool to have. I do have the official Volvo wiring document 'Volvo C30 S40 V50 C70 Wiring TP39167202.pdf' which is proving to be extremely useful once you've wrapped your head around the wiring schematic methodology.
Clan, That's a great piece of information to have, I didn't realise that the CEM got so hot! Also with all this hot muggy weather we've been having, I'm sure that it hasn't helped at all! I'll have to get on to my local Volvo service centre and see what they can tell me with regards to these CAN connectors!
Unfortunately I believe that these problems all stem from the sunroof. When the drains in the A pillars get blocked or the off side pipe separates in the centre where the small pipe barely inserts into the big pipe, I get a swimming pool in the back offside footwell which in turn raises the humidity in the car and then moisture gets into places it shouldn't. However I've not had a pool in the back of the car for a while now since I figured this out. However if I take the car through a carwash sometimes the volume of water through the drain pipes is greater than it can cope with and a get a little dribble of water inside the car down by the bonnet release lever. That's an easy fix though, just don't go through certain car washes
Thanks again for your insights, the wife and I love our Volvo and would hate to have to part with it! It's been though a lot with us, we drove it to Gibraltar and back on a 2 week road trip to get married there, we've been all over Europe in it on road trip holidays, it's still relatively low mileage for the age at just under 110K. Zero rust, best car I've ever owned (electronic gremlins aside).
Greg.