I got back my Mac computer on Monday. This is the end of the line. It's working fine now, but if it dies again, seriously dies, that's it. I had a two-year warranty on parts and repairs and my warranty just ran out. I could have renewed it for another three hundred, but as far as I'm concerned if it dies I'll just buy a new, non-Mac computer.
This time it was the "logic board" which I think is pretty much what they used to call the motherboard. Since we've doubled the memory, replaced the hard drive, upgraded the operating system and now replaced the "logic board" there really isn't too much left to replace.
So this may be a golden age of laptops for me, or I'm going to chuck this and move on.