if you're looking for a polish, don't get something that's going to penetrate too deeply because you're using it on a plated surface. just look for autosol, flitz, maas, simichrome or similar non-abrasive polish. as far as the threads, using a toothbrush is a good idea, but you can just use warm soapy water there, and then follow up with polish when dry if you want. none of these polishes should be used on o-rings, just use vaseline there, and honestly if you want to put something on your threads after you've cleaned them out and polished up everything, just put a dab of vaseline on them too. if you really want to make another investment, then grab some food grade silicone lubricant for all threads, o-rings, etc., but a little vasoline on plastics, rubber o-rings, and threads, and a good mild polish like those mentioned above for everything else will keep you're setup in top shape. that's it.