I have a mid-2004 PowerMac G5 2.5GHz Dual Processor, M9457LL/A, PowerMac7.3. The machine has a "bad processor", according to my local Apple Authorized Repair shop, to whom I paid $55.00 for a full diagnostic. I believe them. The machine will only boot via open firmware. (The CPU overheated during an "upgrade" from Tiger to Leopard. )

Everything else works on the machine; it's just the CPU that needs replacement...and it's my intention to replace the entire assembly, by which I mean the daughterboard that contains the two G5 processors plus the liquid cooling unit. I've taken the unit apart to the point wherein I have easy access to the eight Torx screws that I'll need to remove in order to remove the old CPU assembly. Now all I need is a reliable source for a replacement CPU assembly.

The reason I'm asking is because I've found a huge variation in the prices of replacement CPU assemblies everything from $90 for used units to $550 for "refurbished" units. I understand the principle that you (usually) get what you pay for, but in this case I suspect that it's not strictly true. I'm just looking for a recommendation from someone who knows of a reputable vendor.