Get the oil off with mineral spirits. Wire brush the top until it feels smooth. You don't have to cut through the brownish patina, though it may happen in places. Then use paste wax. Waxilit is good for machine tops. Dunno what it is exactly but I know it's a European thing. You can get a rubberized emery block... it's like a pencil eraser but black and loaded with fine abrasives for cleaning oxidized ferrous metals. In the states it's called a "Wonderbar"... I think it's made in Germany.