Hi, i have one of the bands beatiful Sovereign Euphoniums and im very happy with it. However, it does have a problem thats getting very frustrating. The fourth valve slide seems to be too small a bore for the tubing it sits in, i presume a previous owner had been applying brasso or similar and over a long period the slide has lost a mm or so diameter. I can only play for a few bars and the vibrations start to make the slide drop, only a little at first but over a 10 minute period it can drop by over an inch. Im constantly having to check it and it is a major distraction. I cant tape it up as i need to be able to remove it to empty, and im asking if anyone has had a similar problem and if there is a simple solution? many thanks.