The Copper Glo msds is avaliable online, might be worth taking a peek at to see what's in it.
I like the FLITZ liquid metal polish that contains "no ammonia or abrasives". Many of the 'best' conventional brass/metal polishes that I have used contain ammonia, so be careful until you know it's definitely safe for use on cartridge brass. Good luck.There is a metal polish from citrus magic called brilliant metal cleaner,they claim its the best brass polish there is.I think it used to be called brite boy.Wonder if it is worth a try.