I recently obtained a King Zephyr (1957) and it has brown spots on it, the largest being twice the size of my thumb. It looks a little like rust and is some what scratchy to touch, it feels the same level as the rest of the metal. I am curious what it likely is and whether I need to be concerned, or do anything about it. Aesthetically I am not concerned at all and feel it adds to the character of the horn. I have included a couple of images, thank you for any help!! Thank you!