Hi Jeapel. I think the right way to go is to polish your heatsinks.
Thats easily done with some finegrained quality sanding paper.
You would need to do that in any case. With Silpads, there is no need to use Thermal grease.
I agree with Steen. It is important that the heat sink surface be smooth. The Sil-pad will actually flow under pressure and conform to variations in the surface ofyour heatsink. Check out the manufacturers website.