protecting sliding mechanism

I have some 4130 steel parts that slide in other 4130 steel parts, but
only occasionally. Most of the time the parts just sit around waiting
to be used. What is the best to keep the surfaces from rusting? Paint
is out, as it would clog the mechanism.


--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."