Very fine steel wool means 0000 ( 4 aught) to ME .
Have used a real copper penny...a real copper end pc for gas pipe works as well..since the one cent pcs today are alloy. Have also used a Brass shell case. Go slow and test a small area . Have used a number of fluids, Ballistol, Breakfree, Kleenbore Formula 3, Kellube, Kroil, G96 ...Even RIG grease which seeps into and down under. Let it sit and use the 0000.