Gav..my genuine 16570 is from a 70's vintage ..
Is your bracelet darker, or the case, regarless it may be oxidation, easy fix.. cape code will remove the oxidation or if you want to go all out a refinishing with a jewelers buffing wheel and satin finishing wheel..
the worse case scenario, is to check out the authenticity of your bracelet if that is the part that is discolored.. as the genuine Rolex 904 does not oxidize to the point of discoloration.. at least mine does not have this effect.. but I know looking at my explorer the ss was re-polished professionally.
hope that helps
AC/L