Find some 0000 steel wool and if you have a Wal-Mart or Ace Hardware near you, get some MAAS metal polish. It is near the cleaning supplies (mops, floor/toilet cleaning) at Wal-Mart. Otherwise look for Simichrome, they are pretty much the same polish in different containers... I believe Harley stores carry Simichrome. You will end up with a mirror finish.
I have also had good luck using the metal polish on the sight glass itself after cleaning with vinegar. If you buy gaskets, soak them in steam oil before installing. I would swap them out with teflon/ptfe gaskets.