found this at the heatsink guide:
Scratch off the old glue from the chip as well as possible, and use some solvent to clean it off completely. Acetone is fine, if you have some. Nail polish remover will do, since its main ingredient is acetone, but it leaves an oily residue on the chip after drying. You can get this residue off with ethylen alcohol. Vodka will do; don't use whiskey, it leaves a residue, too 🙂. Tennmax (manufacturer of the Lasagna) recommands Toluene-based Carb Cleaners. These are very effective, but toxic and highly flammable.