A have a slight anoying problem that won't go away my bach strad cornet valves stick now and again. it happents to all valves presently it is the first valve. I have cleaned and dried the valves and casing before oiling. It doesnt hapen unless i am playing the cornet and it coems and goes. I have been offered free valve lapping from the respectable technicians that recently refurbished the cornet, however i know there are mixed views on this. Can anyone offer further advice on why the valves may stick or on having the technician look at the valves.