Heat sinks just "pop" on. But ya, you should use some thermal paste too. You can get that cheap at Radio Shack or similar store. Use a VERY thin layer of thermal paste spread onto the motor or heat sink and then just pop it on. Make sure there is no label or sticker or what not between the motor/paste/heat sink when you put it on. Be careful of the thermal paste, it gets everywhere and does not come off easily.
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