Tentacle, if you're going to remove the IHS, use some form of liquid metal - though it can cause shorts, it's the best for that.
That being said, only remove it if you're going to apply a liquid cooler (a real one, not a closed circuit one) directly to it. If you're just replacing the thermal paste, don't bother, just get MX-4, slap it on there, and not worry about voiding your warranty for 3-4 extra degrees.