I spent about 5 years professionally working on video game consoles. I fixed literally thousands upon thousands of 360's, and ps3's, ect. First gen 360's (xenon) and later but essentially the same (zephyr) mobo's where the most common to suffer RROD, but every so often I would come across a bone stock one still chugging along. It got better as the mobo revisions went on, and IMO Jasper was the most reliable 360 ever made, even moreso than the slims that came after them (although they were pretty good too). Anyways, the RROD was a combination of things. The lead free solder was definitely at the heart of the problem though. The first 360's didn't have big enough heat sinks, and the chips were far less efficient, and the heating up and cooling down of the lead free solder would make it brittle. Sometimes tin whiskers were thought to be suspect as well and most likely could have been! The good news was that 360's became pretty reliable after being properly fixed, unlike ps3's (which have a shit ton of their own problems, including YLOD, the ps version of RROD) which never really liked being fixed and staying working.