I think the important point here is that rust is mostly a cosmetic issue and not a structural issue with stainless marine parts.
The term "Stainless"... is likely a confusing word. They call it stain-less but it is really not "stain-free". There are many grades of stainless steel. My understanding is that the more stain free the metal is, the softer it is. In cutlery, the best knifes are often carbon-stainless which are not bright and shiny. That is because the stainless will not hold an edge as well. For many uses a harder metal is required, so there are compromises. Anyway...in marine metals, often there are varying amounts of discoloration to the "stainless" materials. This is not normally a case where they will rust through. Generally it is a surface rust that is similar to an oxidation. It can also be caused by carbon tooling materials that has stuck to the metalwork from the manufacturing processes. Sometimes this type of discoloration can be prevented by a process called passivation. This helps to remove bits of carbon tooling debris that sticks to the stainless. Most all marine stainless metals go through this process. We sometimes find materials that have not been passivated properly and they will bleed rust at a higher rate than we desire. Especially where threads have been cut. This will continue to rust until the carbon dissolves. The actual stainless parts should not continue to rust after that.
As an industry note, my understanding is that some manufacturers of sailboats actually give a bottle of rust stain remover with every new yacht for this issue.
We have found that Magica works well to remove rust stains from hull surfaces and metalwork. I have personally tried many different materials on rust stains with little effect. Upon the application of the Magica... the rust stains disolved before my eyes!