All stainless rusts, including internally at room temperature.  That is
why it is called Stain "LESS", not Stainfree.
    The only stainless that I have ever seen that did not rust was on a
newer Swan (swedish built) sailboat.  8 Years in the caribbean and the
stainless looked like new, without cleaning and polishing.  The stainless
on most other boats in the tropics look more akin to exhaust pipe.

John
87 Westy SVX
91 GL jdm TT conversion (looking for stainless exhaust pipe)