i have a Yamaha Xeno 8335RGS, its the special edition Bb. bought the horn 4 years ago, been playing it ever since and i love it....but. my valves feel "mushy", not quick responsively and seem to lag a lot even after a fresh application of oil. what is causing this? i had the horn cleaned almost 2 years ago, springs replaced and still no change. whats up with my horn?!