Getting the green crust off a silver plated horn

[NATHouston]

I found this instrument in my inventory in this condition. It plays perfectly fine, but I would like to clean up the exterior, especially the green residue where the silver plating has come up on the 3rd valve slide and where the thumb goes. What's the easiest way to do this? Or is this something that I'll need to send to the shop to have done?

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