Valve oil actually can (and does) dry out and can leave deposits that will cause your valves (or rotors for you Horn and Trombone players) to seize up over time. You should use 3 to 4 drops of valve oil in each valve first thing before you play each day. If you know you’re not going to be playing for awhile, continue to take your horn out and move your valves regularly once a week for 30 seconds. Always store your horn in a cool, dry place. This coupled with proper emptying of your water keys and regular cleaning and your horn will last as long as you need it to!