And to add to HNC's reply: If you want to bond the heatsink to the ESC case, use thermal
adhesive, not simply thermal
compound. The link for the Arctive Silver adhesive is:
http://www.arcticsilver.com/arctic_s...l_adhesive.htm
Be warned, it is considered permanent. If you use normal thermal compound, you'll have to find a way to hold the two parts firmly together and not move around (hard to do win an r/c car).