The initial problem is exactly the same as the current problem. I don't suspect that the GeForce 8600M GT was ever bad in fact, but considering how common the graphics issue is with these models and the number of ways in which a GPU problem can manifest itself, I performed the BGA reflow to rule it out as a possibility. Based on what i'm now seeing, i'm confident that the issue is in one of the smaller components of the board and a MOSFET certainly isn't out of the question.