it must have been a very strong bleach to have stained stainless steel
however you could try T cut that you use on your car it may work if not try brasso but if using either make sur that when marks are gone to do all of the sink as it will look odd
ORAC60
Every so often I always clean my stainless steel sink with bleach as they do tend to get tea stained etc, are you sure this isnt the case? I would try cleaning the whole sink with bleach, mine comes up gleaming