I swapped hardware with a buddy of mine and I now currently have the brass/gold hardware and it's starting to dull. I was wondering if anyone else had this problem and if they fixed it how so? Can it be polished or am I just SOL?
I belong to a few SIG groups on FB and posted your Q yesterday.... no help as yet. Sorry.
If I hear back from the SIGophiles I'll post the response here.
I have had a similar problem with some guns I collect. I have a number of pre-2006 Taurus PT9XX semi-autos and any gun in that family could be bought with gold plated controls. The plating is thin and, although not prone to tarnish it is prone to wear. You can achieve some renewed luster with anti-tarnish products targeted at jewelry but almost all of them contain some abrasives which will just accelerate the problem.
On the Tauruses the metal that was plated was not even stainless, I assume because of the chemical needs of the plating process. Unfortunately, while I am free to consider the bling on the Tauruses to be a bug and not a feature, for you it is a part of the special appearance of your pistol. I have bought stainless parts over the years from people parting out similar pistols on gunbroker and have also considered having the parts stripped and cerakoted (which is how I know the condition of the metal underneath the coating). I would expect in your case, if you wish to maintain the look of the gun you would have to find someone to replate the gold and then unless you put the gun away the process would just begin again