Bruie,
Behind the jets on the vast majority of wands should be a combined filter/anti-drip valve.
Inside the filter is a ballvalve and spring, which can be accessed by unscrewing the input end. Carefully dissemble and check the ball and seat for pitting/contamination. The spring may have weakened with age, requireing replacement.
These valves are designed to release at a fairly low pressure, so anothe cause of dripping, where the valve itself is functioning correctly, is a slight leakage past the trigger valve on the wand.
John.