If you want to use all of Artic Silver’s potential, clean all the old goop off your HS and then lap it. You should read the info at Artic Silver’s Site. Think of it this way, where the thermal compound is really important is filling in the microscopic surface imperfections in the surface of the HS. You can’t get the old goop out with just solvent and a rag. If done properly, you will drop 5 to 7 degrees.