Instrument in question: 1989 Selmer Bundy. It was my first ever real instrument, and it has a huge amount of sentimental value. I have an instrument that probably was never cleaned correctly. There seems to be a hard mineral build-up in the interior of the tubes. The lead pipe, tuner slide, and the valve slides, and probably the main bell tube are all affected. The valve action is not affected by this build up, but all of the tuning slides are, slightly -- that is, it's not entirely an "internal cosmetic" issue. It's a whitish, very hard mineral material that does not respond to soap or hot water. This is an older instrument that has seen better days. I'm not concerned about the outward appearance of the instrument as it's terribly bent and dinged up. However, I'd like it to play the best it can. External corrosion (and petina, etc) is forgivable, mechanical corrosion is not so much. That said, would a diluted vinegar bath help to dissolve this internal mineral deposit problem, and if so, will it cause any secondary corrosion, (or petina) on the internal tubes that might interfere with the action of the instrument? Is there a better way to remove these mineral deposits from a decrepit instrument?