Never Never Never Never use steel wool around or on circuit boards!
You'll cause problems because fine little pieces of that steel wool will find it's way underneath components and cause short circuits.
Just go to the office supply store and get a common large ink or pencil eraser to scrub the edge connector foil with. Then go over what you just scrubbed with a paper towel or clean rag moistened with 99% isopropyl rubbing alcohol.