i don't use anything at all. i never have. oh sure, i rub it clean with a wonder wipe when i change strings, but that's all i've ever done to a fretboard, ever. i've never had a "dried out" fretboard. over the years, dozens of guitars, many of them abused more than they deserved. those boards are often kiln dried. when they're not, they're air dried. but still dried. on purpose. when they are dried, it is because water, not oil, was allowed to escape the wood. why would you add oil to replace water loss if that was a concern? it certainly can't be expected to act the same. they are only similar in that they are both liquids. if a piece of wood cracks or deforms due to extreme dryness, neither oil or water will bring it back. most of the time i think the whitish color people attribute to dried out rosewood is probably salt and skin. maple boards don't do it. furniture doesn't do it in anywhere near the timespan people claim a fingerboard will. oiling the fretboard is hokus pokus
