I've had to send in my Xbox 360 for RRoD, I've had to replace my cooling fans twice, installed new 80mm fans to the top of the Xbox (drilling holes through the top) to get proper cooling, then when the motherboard finally died I had to swap it out with another one from an Xbox 360 that had a dead DVD drive ( it didn't spin). Boy was that fun.
First: replace the motherboard with the old one. The old one needed the new heatsinks to make it work, so that was loads of fun getting those off the new one and onto the old one. Then I had to swap the PCB off the broken DVD drive into the new DVD drive so it'd accept games (the PCB, again, wasn't the problem, the motor was). Then I had to take back off the heatsink for new thermal paste. RAWR.
And it's got four rings again. Sigh, time to reinstall the 80nm fans.