Open it up and fix the GPU's heatsink problem....it's an inherent design flaw that Apple ignored by glopping thermal compound on the GPU so the heatsink made contact with it...over time the compound will eventually spread outward and will no longer make contact with the GPU, thus overheating it and shutting down the computer. Luckily, my compound was still making contact and I wasn't having any problems except the fact that it was running a bit hot (55* C).
I just took my recently acquired 15" 1.67 DLSD/HR apart to clean it out and replace the OE compound with Arctic Silver, and sure enough, the heatsink doesn't even make contact with the GPU. I measured the airgap and found it to be 0.8mm (really Apple? Really?), in which there are numerous copper shims on eBay in that size. I ordered me one and I am going to fix mine. Just remember, it's a bit of a job to pull it all apart.
Here's the one I bought, I think they are the only ones in the US on eBay that sell them cheap. I would measure the airgap before ordering though, they may all be different. All you have to do is attach the heatsink assembly to the logic board. with the mounting screws around the CPU and GPU, then you can measure the gap.
http://www.ebay.com/itm/320747909222
I just took my recently acquired 15" 1.67 DLSD/HR apart to clean it out and replace the OE compound with Arctic Silver, and sure enough, the heatsink doesn't even make contact with the GPU. I measured the airgap and found it to be 0.8mm (really Apple? Really?), in which there are numerous copper shims on eBay in that size. I ordered me one and I am going to fix mine. Just remember, it's a bit of a job to pull it all apart.
Here's the one I bought, I think they are the only ones in the US on eBay that sell them cheap. I would measure the airgap before ordering though, they may all be different. All you have to do is attach the heatsink assembly to the logic board. with the mounting screws around the CPU and GPU, then you can measure the gap.
http://www.ebay.com/itm/320747909222