Stainless absolutely will rust. If you have ever owned a boat, like I cited above, you know that keeping it clean is an ongoing proposition. Cleats, chocks, screws, and other items made of stainless will rust for sure. Certainly not as bad as regular steel, but it can range from surface rust to pitting.

I've probably had 30 boats over the years and haven't owned one yet where the stainless was "stainproof." Obviously stainless fittings on a car are going to be less prone to this problem, but not totally immune.

Don