There were some small discoloration spots on my new ROJET BSE RE and my Randy Smith Spinner was tarnished. The engine instructions said the engine could be cleaned up with Mother's aluminum polish. Hey. I've got some of that. So, I gave it a try... Now, how do I get the black residue out from the cooling fins and the like? I tried a tooth brush but that just smeared it around. Is there a solvent that will clean it off? Mineral spirits maybe?