Apart from cutting through rust and moisture, most of the penetrating oils in the market can work on mild grease and oily layers as well. But you will need to use a lot of it on a surface to clean them. After spraying a generous amount of it, simply use a steel brush or steel wool to get the grease or tar off. Leave it like that for a few minutes before wiping the surface with a clean cloth. Because the manufacturers of penetrating oil are trying to increase the utility of their product, they have been coming up with better cleaning agents recently.