After a carefull cleaning with a toothbrush and water the CPU has recovered. I ran it in the old motherboard for several days without problem.
I cleaned the motherboard and put it back in today, but I'm not 100% sure if it's OK yet or not. I've had one mysterious crash, but it seems to be running fine now.
All of that didn't fix the temperature problem though, it is still registering as too hot.
Jay