I love roloc discs but you have to watch how you use them. Ford has determinded that the wore off abrasive is a major cause of engine failure. If they do an oil analysis of a failed rebuilt engine and detect any material from a roloc disc they void the warranty. They will also remove metal, fast! You won't have too much problem with them on cast iron but they can screw up aluminum with a quickness. I usually scrape as much of the old gasket off as I can and then use the pads for the rough stuff and surface prep. That saves you money, too. Last time I bought any they were around a buck apiece.