The MacBook Pro 17" would boot to a gray screen or if left alone for a while it would boot, but eventually crash. The area around the GPU memory was warm and the bolts connected to the GPU heatsink were very hot to the touch. Swapped the left fan with the right to see if the fans were working. The fan failed plugged into the left location also.
Simple repair, just remove the bottom plate, unscrew the fan and gently pop the power connector off. Installation is the reverse. Plus a lot of dust cleaning.
Expect to clean out a lot of dust.