Rust on stainless? Must be a poor grade of stainless(303,302,416) this group does have some carbon in it,  anything with carbon will rust .  The higher the carbon content the more rust. Examples 4140 alloy steel 40 percent carbon.  Stainless shall hold a stain because is has a course core,  any type of rusted parts placed onto stainless or aluminum shall absorb the carbons and iron oxides.. how do you stop this ,it is called refinement of finish(smoothing top of surface) polish it to a resolution shall put the brakes on the extreme factor.

Clean the core stain out with Clean IT  ,polish it with super shine 30.