Over the last few months I noticed that all the valves on my euphonium, particularly 2nd and 4th are starting to stick more and more. It's slightly worrying considering I bought it new in December. I regularly clean the instrument and use valve oil, but one of the teachers at school, who used to play euphonium said maybe I was applying pressure from the side which was making them stick. Does anyone have any idea how I can solve the problem? It doesn't happen all the time, but I've started to play much more quietly at band as its starting to make me a bit nervous especially in fast passages in case they stick! Am I maybe holding the instrument at the wrong angle?? Any help much appreciated.