Hit the cover with a green scotch brite, soak in hot tap water with dish soap. I like Ajax brand soap because it's super cheap and works as well as dawn. After you let it soak for about 5 minutes, rinse with warm water, clean with alcohol, then repeat the whole process until you don't feel a slick coating on the ball in the soak. It takes a while, but it's the best at-home deep clean I've found. Also, it seems that the scotch brite brings the finish to a little more even reaction, IMO.