OK - the VRAM chips I've highlighted with blue circles - and I suspect the ones I've highlighted with green circles may be VRAM chips with thermal pads over them.
if the heatsink doesn't contact them directly, you need to use themal pad, not TIM, to fill the gap.
Here is another pic of one apart. you can clearly see the white pads on some of the chips, and corresponding heatsink positions.
Edited by latelesley - 3/31/13 at 2:53am