I generally use my die grinder with 3M Roloc Scotch Brite discs. There are cheaper versions from other (Chinese?) manufacturers that work about as well http://solutions.3m.com/wps/portal/3...glWMP2M1LZT2bl

...or even just the paint removal wheels found at the big box stores will make short work of those gaskets - and wont hurt the sheet metal oil pan.