I would try: Scrub with and then soak in vinnegar. 10 min Rinse Using water and baking soda to make a paste, work this in to the band and case back. This is abrasive and may scratch, use your judgement. Let this sit 10 min. Rinse very well, any left behind will show as a white residue. Wash again with antibactrial dish soap. I've been skipping the baking soda when doing my metal band work watch and still getting good results. YMMV I might do this once a year.