So the fix lasted until I got home last night. Initially the system worked fine, but then it started locking up. It installed an update from Micro$oft, but eventually I had the 3 lights RRoD again.
Solder problem still exists, tried the towel trick – no luck. Going to pick up the 360 Slim today, and if I can get the old one fixed, donate it to a needy gamer… lol
Figure I’m going to pop the old one open again, visually inspect the solder points and see if there’s anything I can do there, reseat the heatsinks again using actual arctic silver instead of ceramique, and then see what happens.