Over in our tech talk forum, a common topic is how to go about removing leftover thermal goop from a heatsink.  Arctic Silver is a common brand to use, and they now have their own cleaning solution.  Mikhailtech reviews it, and you should read it if you are wondering just how to remove that old paste from your heatsink.
“Given the minor time investment in cleaning the heatsink, I was pleasantly surprised by ArctiClean’s ability to get rid of the leftover compound. It’s not a miracle solution; it took several “passes” to get most of it off. But, as you can see the difference between plain rubbing alcohol and ArctiClean is quite noticeable. It’ll still take some time and lots of rubbing to get rid of all the paste, but it’s a great start. I also used ArctiClean on a copper heatsink which used a ceramic-based compound. It came off completely with the cheaper alcohol and ArctiClean didn’t account for any noticeable difference. It seems that the degree to which rubbing alcohol will work compared to ArctiClean depends on the compound in question. Arctic Silver, as we saw earlier, doesn’t come off too well with Isopropyl, but white paste does. I then decided to clean off a CPU which was placed below the aforementioned copper heatsink. It too had a ceramic compound on it.”

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