The number on the valves is NOT the serial number of the horn. The serial number is on the bell just above the collar connecting the bell with the bottom bow.The serial number will be something like 1065HGS-xxxxxx where 1065 is the model # denoting euphonium, HGS describe options (Heavy bell, Silver with or without Gold trim, etc,).
I also agree about cleaning. The horns come with very tight valve tolderances from the factory and also tend to have construction grime from the soldering and buffing inside the tubing. A good cleaning with Herco Spit Balls something like a QHR (Quick Horn Rinse) does wonders. Follow up that by thorough drying. If the horn had been played quite a bit, calcium deposits on the pistons will tend to cause some binding. There are different approaches to getting rid of scale and plaque on the pistons. If you are uncomfortable doing that kind of work, contact a technician.
Doug
Adams E3 0.60 Sterling bell - Prototype top sprung valves
Concord Band
Winchendon Winds
Townsend Military Band