The retail heatsink will come with three parallel strips of a grey material pre-applied to the bottom; that is the thermal paste. It is ok to use. The key in mounting the heat sink is to make certain that all 4 push pins are solidly inserted into the mobo. It is best to do the insertion with the mobo out of the case so you can look at the back to verify that they are all in. It goes best if you push in diagonal pairs simultaneously. Before you try to push them in, carefully read the instructions that came with the cpu. Make certain that you know how to twist the knobs before insertion. Read both the installation and removal instructions so you can see how the attachment works. If for any reason, you need to remove the heatsink, it is best to clean off the old material with some alcohol, and re-apply some new paste. If this is done badly, your processor will run hot, but don't worry, if it gets too hot(unlikely), it will just shut down to avoid damage.