Use the power of ice to remove dents in a horn. If you live in a cold climate, you know frozen pipes bursts. That is because water expands about 9% when it freezes. You can use that property to pop out dents and expand crushed tubing in brass instruments with a little luck. I had a crushed leadpipe on my old horn that I couldn't reach with a pushrod (out of a V8 motor, worked like a charm with its rounded end!) So I filled the leadpipe with water, sealed both ends at the mouthpiece receiver and first slide with a rubber balloon (or fingers cut out of a latex glove) and pipe clamps loosely tightened. Put horn into freezer for 4-5 hours or until your sure the ice is solid. Take out with a towel and set bell down so it will drain out. You will notice that the ice has expanded out of the leadpipe. The amount of expansion out of the leadpipe is proportional to the amount of outward force it exerted, ie, if no ice came out, your leadpipe will probably have burst, or at best straightened out completely! Remove seals and let water drain. With any luck, your dents or crush zone will have been pushed out by the expanding ice. If it didnt work, you can try sealing the ends with a more rigid device like a cork or hard plastic cap. Be advised that if the water has nowhere to expand, it may rupture your leadpipe or brass tubing, so keep that in mind. Hope it works, you really have nothing to lose and your horn will be cleaner than when you started.