I have a NX 4510 and as soon as I release the back pressure on stick the loader falls. To trouble shoot, I have switched hoses from the bucket curl cylinders to the raise arms cylinders and had no down drift. So I have concluded that the valve spool body is leaking internally. I have no oil leaks externally. Went to dealer and the only part they offer is a total valve spool body replacement at $1500. Looking for any advice on a fix without a total replacement.