Common sense 101: Lubrication is based on surfaces being isolated by a film of lubricant. In our case, valve oil is pretty thin, there is no pressurized system to "relube" and we are blowing moisture and aerosols into the horn while playing. We are not pushing the valves down straight and the oil has a tendency to evaporate, leaving only the moisture of our breath and the sludge from the aerosols in the valve casing. Water does not lubricate well. Petroleum based oils do a decent job for about 1 day. Synthetic oils last longer, but the sludge stays in the valve casing longer too! I will say, if we take good care of the horn and oil daily, it doesn't matter if we oil before going to bed, after brushing our teeth in the morning, before, or after playing. If my valve stuck in a concert once, I would be really mad that I didn't lubricate before going on stage however. If YOUR valves stuck in a concert, you can figure out what the rest of the world would think.......... Now go do the right thing.