I don't buy any of this ammonia BS
Ammoina degrades Zinc, Brass is -- Copper and Zinc.
Cartridge brass is a composite, an alloy of several metals including Zinc. But not all cases are the same, the alloy varies with each maker. Here's a partial list;
The ammonia evaporates in hours, the ammonia content of Brasso becomes inert after it evaporates, so a three year test was moot within hours of application.
A true test would be to apply Brasso too group X of a single lot of brass, then continue loading them with the remaining lot and watch for any early failure,
My take on it is there is simply too many other things to put in tumbler media that's NOT harmfull to cartridge brass even from the start.
So I guess if ya throw some Brasso in your media and run the vibrator for a few hours before adding brass it's not going to hurt much.
But why use it? There's tons of other stuff to use.