You haven't discovered WD-40 before???
WD-40 is to lubricating and de-rusting as duct tape is to holding things together.
Once I fired a Mosin Nagant 91/30 with lots of corrosive ammo, then left it in a humid basement for a month without cleaning it. WD-40 just dissolved the rust and it flowed out of the barrel. I had used it before, but this amazed me.
I've heard that WD-40 can be corrosive to some finishes, though.