Bradsknives
Master
City foot patrol cops used to vasoline the inside of their leather holsters to try to keep the rust problem down to a minimum. Like others have said, I never store a blued gun in a holster.
I'm a knife guy and I can tell you that Vasoline is the worse thing you can put on a knife/ blade. Vasoline will trap moisture and eventually ruin the steel. I saw the end results of what vasoline can do to a collection....a $50,000 plus knife collection that basically was worthless after storing them with vasoline on them. I wouldn't think it would be a whole lot different for a gun.