i tried this rather unorthodox method of preventing metal wares (exept guitar strings) on my guitar from rusting. that is to apply lip balm or lip gloss or wax (preferably those which u got from the dentist to apply on ur braces). it works, and they r transparent, some like lip gloss gives a little shiny feel, non-oily and stays on the metal wares for reasonalbly long period of time. i rationalised that these lip balm or wax are waterproof so they prevent moisture from reaching the metal wares hence minimising rust or tarnishing. i heard wax can also minimise strings from choking while tuning!