I have a 4ft FEL on my Kubota B7200. The boom will not stay up with the bucket loaded or unloaded. I checked the pressure relief valve setting, it was set low and reset it to 1500psi. The bucket still lowers at about 3/4" per minute. I dead headed a pressure gage into a working port on the valve and found that when the valve is opened the pressure is 1450 psi and when the valve is closed the pressure in the line drops down to 0 psi. Could the valve spools be worn to the point that the valve will not hold the pressure? What elese can I check?