You DON'T want t use WD-40 on a horn. If Bryan's repair tech/friend suggested that, then Bryan needs a new tech. WD-40 is flammable, and if the horn has to go to the shop eventually after unsuccesful attempts at removal, a legitimate tech will use a little penetrating oil first - we use non-flammable stuff, such as "PB Blaster" (auto-parts store) first - then a little heat from a torch to activate it. If there's WD-40 in there, the flames that start shooting out are not fun. If there's some penetrating oil in there, Bryan's suggestion of lightly tapping on the outer side tubes is OK, but a rubber mallet won't be too effective. However, finding a wooden or rawhide mallet outside of a repair shop or school bandroom may be difficult. You don't want to use a hammer with a metal head.
Regarding the sticking valve, the first thing you can try would be to remove the piston and bottom cap. Then, roll up a piece of paper towelling into a cigar shape, run that through the valve casing. A LIGHT solvent such as denatured alcohol or fingernail polish remover on the towelling may help pick up any particulates. If you use a solvent, follow by running a dry paper towel through the casing. Also, wipe off the piston. Re-oil, and try. If it's still sticking, then it has to go into the shop. And no, you can't help the matter by using steel wool or a belt sander on the valve. You may laugh, but I've made a lot of $ in my shop off of peoples' attempts to pull slides (using hammers, belts, rope, etc.) and repair sticking valves themselves.

Last Edited By: lastchairtpt Sep 4 09 7:36 AM. Edited 2 times.