Do I need a new logic board for a new heat sink?

I agree, we need to figure out what the actual problem is, and go from there. I've never known a computer to specifically "need a new heatsync", so I doubt simply replacing a heatsync would end up solving much. Maybe re-seating the heatsync with thermal paste, but the stated need to replace it sounds very odd.

Thanks for your help. Well the Apple guy didn't actually look inside it, I just told him what I'd seen when I had a look in there myself to clean it out. The top third of the copper C shaped thing (which I think is the heatsink?) is blackened, the rest of it is still copper.

I took the Macbook in due to constant overheating and thermal shutdown. Anytime I watch a video/doing anything in flash or processor intensive, it gets ridiculously hot (110C+) and shuts down. It's got to the point now where it shuts down after about 1min of flash video. Thought it might be the fan so, like I said, I opened her up and cleaned her up, but made no difference.

The Apple guy did tests that they do and just concluded that it needs a new logic board and heatsink, I just wasn't sure if I could have the heatsink without the new logic board.

Thinking of cutting my losses and throwing her in the bin...

Alex, to early for the bin.... disassemble it and post some images on here. Those Mac guys on here are a great bunch of people and I am sure they are going to help you with this.

The heatsync could easily just need the old thermal paste cleaned off, and new paste applied. If the heatsync has been taken out at any point, which would break the thermal paste seal between the chips and the heatsync and cause heat to not conduct properly, that could easily explain the overheating. As for the fan, verify it is on when you have the top off of the laptop. A program like iStat Pro will also show fan RPMs. And make sure the heat sensor connectors are in place, because the fan will never know to spin if it doesn't have a connection to the logic board.