After all of that, I figured I'd update the OS to see if it performed any better. What a nightmare that's turned out to be! Why can't I leave well enough alone?!

The install/update goes to about 60% then fails and restarts. It gives me the 8002F14E error code. From what I've read, the Bluray drive is bad, so I'm going to buy one from eBay. It won't take discs, so I would think that's a problem. New ribbon and power cables were in the box already, so I've ruled them out.