This is the first valve to an older Holton student-model trumpet.
The little bump (shown with arrow) is supposed to mate with a little notch inside the valve casing, which keeps it rotated properly for playing. I can't seem to get it to catch, though, and so it rotates around in there and makes the trumpet unplayable. The other two valves work correctly and I can't figure out what's wrong with this one to make it fail in this manner.
Looking to avoid a costly repair on a not-very-valuable instrument. Thanks for any help!