I would imagine that the issue is similar to what happens with 360's (which I have a ton of experience repairing). The PCB under the CPU/GPU probably warps slightly from heat buildup and causes a disconnect with the IC. The heat gun method works, although it is not very precise. It is probably not worth it to do it yourself, but if you could locate someone with a proper hotplate reflow station you might be able to fix it more permanently. Other than that, I am going to have to refer you to someone with more experience with repairs on the PS3.