Unknown Verge Fusee

SkunkPrince

3M Tarnishield is used by wind instrument repair technicians, and might work out if the case can be separated from the movement. It is water soluable and plenty of these technicians dilute it. I've polished my silver-plated trumpet with a new, clean, white towel and diluted Tarnishield.

So it might be worth considering.

Waltesefalcon

Tarnishield is sold under the Scotchgard brand by 3M.