not that this will make much of a difference to anyone now ,
i have seem to have made a fix for the g84 issue , i used double sided tape on the gpu and cut it out around the gpu and when sandwiched between the heatsink and chip puts pressure on it stopping the bga from unsoldering.
i had to reflow every day because the gpu would come undone , i have been running for 2 weeks now with no issues.
i can post pictures for anyone interested.
Just control the system temperatures with the likes of UltraFan or SMC Fan Control, try to keep it below 70C on the GPU when possible I have an Early 2008 15" Penryn 2.4 MBP with well over 30K hours uptime and no indication of GPU failure. It`s extreme temperature and rapid fluctuations that kill these GPU`s prematurely due to the manufacturing issue, keeping the temperature stable ail go a long way to help longevity.