56 power steering control valve problem

I hope someone can help me with this problem or give me some suggestions. The power steering control valve was leaking on my 1956 thunderbird so I bought a rebuilt one from concourse parts and now it is leaking again. I know there is an overflow tube on the unit but my mechanic put the unit in and all he will say is the valve is leaking. Could it be a bad valve? or could the lines going into the valve be worn enough to have the leaks come from there? any suggestions would help, THANKS.