even the grease from your fingers can make the barrel rust. always give the gun a wipe down with an oily rag all over the metal work to stop this happening or spreading. dont soak it in the stuff. just a lightly oiled rag. 3 in 1 oil is just as good as anything else out there. i wipe my riflles down after every session. they still look like new.
dont store them in damp places like a shed or garage. and if they've been out in the cold, keep them in their slip until they're at room temperature then wipe them down. if they get wet in the rain, take them out of their stock and give them a good wipe down all over. its easy to keep them looking nice. it's even easier for the to look bad. it only takes a couple of minutes to give them a quick wipe. they'l last years then.