I'd recommend against using either alcohol percentage until someone more knowledgeable than I recommends it. 99% will suck the moisture out of your skin and you need proper ventilation. I use it to remove adhesives and paint. I have no idea what it'd do to plating. EDIT: Also note that alcohol will discolor rubber mouthpieces, probably some plastic ones, too. 99% IPA might melt one.
It's highly probable that you're looking at tarnish or worn plating, not mold. I'd think of mold on pads or inside your case. Possibly in or on the body of your horn, corks, or felts. In other words, porous stuff, not metals.