The thermal pads on both machines basically turned to glue...

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The thermal pads on the GPU and system controller are the normal white, non-adhesive pads used since ages past. On the processor (of the DVI models, not the VGAs), however, they use an odd substance that actually does adhere the CPU to the heatsink. Removing it requires the use of a razor blade and loads of caution, something that must be done every time the logic board is removed. Replacing it is difficult, because it can't reliably be reused, and normal thermal compound can't be used because the contact surfaces between the CPU and heat sink aren't completely square, which is why the odd thermal stuff is used in the first place. So, I found that the blue-ish thermal compounds from the iceBooks are best here, as it's reusable and contours itself as necessary. It's the next best thing to the original stuff.