Check the function of the control unit during the test with clean water. The main valve must close completely. If it drips from the nozzles when the main valve is closed, it is likely that the valve ball and the ball seat are worn. Check and change if necessary.
The boom section valves must also close completely. Open the main valve and all section valves with the pump working. When the return hose from the constant pressure valves is removed and the housing drained, no water must appear on the valves. If the section valves are not completely sealed, the valve cone should be replaced.
Finally all movable parts of the control unit operating handles should be lubricated with oil.