Use BRASSO or similar can of metal polish and a soft cloth using a circular motion, just as you would cleaning brass, rub the scratched side,it takes a long time so be patient,wipe with clean cloth after about 5 mins,hold it up to the light to see the improvement then do it all over again until you are happy with the results,use a fresh portion of cloth when you do the second rub,you could also use toothpaste in the same way,rinse the parts in soapy water when done.Good luck.
Rich, June 2006