that happened to me recently for the first time, and i had used it hundreds of times before.

it was pedal axles. not only did they turn black, but they gave off the worst odor i hadn't smelled since working in the oil patch in hobbes, new mexico. sometimes, out among the producing wells, you can smell h2s. just a few parts in a million will smell like rotten eggs. a few more parts will kill you. that's exactly what those axles smelled like after retrieving them from the naval jelly. i wonder what happened that time that hadn't happened before...