We bought a couple of Besson Sovereign 928 large bore cornets for our principal players recently, great instruments, wonderfully responsive and above all easy to play, but while one has been trouble free the other has an infuriating tendency for the valves to stick in slow lyrical passages. The valves are fine on runs, scales etc waggle up and down faultlessly and then stick when you are playing slow melodies. Both our principal Cornet player who reverted to his JP 379(?) for this afternoon's performance and later this evening I myself had this issue despite cleaning the valves throughly and re oiling. Any suggestions gratefully received..