I am using the same heatsink, Gigabyte 3D Rocket Cooler. The heatsink surface is pretty good from the factory. I buffed mine out with some brass polish on a flat piece of glass to make sure there was no gum residue from the protective tape.
It shined up nicely and the ammonia based brass polish washes off with water.
I am using A.S. Ceramique on an XP2500+ running at 2.2Ghz. It works great.
Instead of using a finger wrapped in a plastic baggy, I put some thermal compound down on the glass and rubbed it in there.
Don't do a thing to the cpu except clean the top surface with a recommended solvent.
I have lapped other heatsinks. Some were warped, others were deeply scored.
Taking care to mount the heatsink properly with the correct amount of compound is critical.
Which processor are you using?