Forward Chemicals Metsol Cleaning Swipes are the best I've found. They are impregnated with something that really does clean TIM and swarf from heatsinks. I used 7 cloths to get my AC Freezer 7 Pro clean. It was visibly clean, and if you rubbed it with a piece of kitchen roll nothing came off, but the swipes kept pulling grey 'grit' out for quite some time. Then I put it all back in again as recommended by AC.