You and 153 are both correct - I don't disagree with either of you in that regard. There's certainly nothing wrong with using gun oil, by any means. There's a reason it is used and marketed for that purpose.I don't see any real reason to switch. I don't think gun oil is that expensive.
Lol, I used to feed my fish Tetra. I had an Oscar who ended up about 3 pounds. He ate all my other fish and then committed suicide by jumping out of the tank (through the plastic lid no-less). Haven't used the tank since.