You may want to get some Renaissance wax and use that on the gun, it's great stuff.
Just because it's Stainless Steel does not mean it can't rust, it depends on the composition of the stainless, there are also magnetic and non-magnetic stainless steels.
I have heard of people with very acidic systems that will cause such issues.
I second Yankee's word's here.
Any metal can rust/oxidize, given the right conditions, even stainless steel - it just stains- less.
My gunsmith of all people must immediately wipe down all guns that he handles or they will start to show signs of rust really fast, regardless of finish. He just has a high acidic ph in his body oils.
Renaissnace wax is good as well as Ezoxx, which you can get in a spray, it leaves a protective wax base behind.
Also Boeshield T-9, it leaves a wax base behind as well - and you can get that at Sears in the tool dept.
Please let us know of any developments.
Good Luck