Thanks. That actually doesn't look too hard after all. I suppose finding the right heatsink will be the most difficult part - what were the approximate dimensions of the heatsink you used, before you modified it?
I'm assuming from the pics that although you dissasembled it quite a bit, this was only to show some of the components that would otherwise be hidden from view, and it should really only be necessary to take off the back cover in order to expose the existing heatsink - is that correct?
Also, I can't help but wonder - it looks like there might be connections between the CPU and conduit, and/or between the conduit and OEM heatsink that, if loose, would aggravate the problem. But I think you said that you had checked all the connections and they were fine.
Thanks again for your description and pics.