I have a brass Holton...and on my slide there is some rusty colored spots. I've shined it, given it baths, used brass cleaner, but nothing seems to be working. I've asked several people what they thought, and got several different answers, including:
>An acid leak, from not cleaning the slide after oiling (slide oil...which I don't use anymore.),
>Water got caught in the outer slide after a bath and ate through the finish, and that I can get a kit to clean it off, and
>The slide is simply rotting. There is nothing I can do about it but get a new horn
(though I've only had this one about 2 years).