[AT] MF 245 Orchard puzzler--help if you can!

[John Wilkens]

My neighbor friend has been working on the power steering of a MF 245 
orchard tractor.  Neither one of us understands very well how the 
power steering control works.  The power steering seems to work fine 
in either direction but when you let go of the steering wheel it 
turns all the way to the left--on its own.
The force to turn the tractor wheels left and right seems about equal 
and normal.  If you tweek the steering wheel just right you can find 
a neutral position where the tractor will not turn by itself, but if 
you shut it off and start it up the wheels will turn left by 
themselves again.  We took the control apart and cleaned it up and 
put air through the ports and put it back together but it still does 
the same thing.    This tractor has the dual steering cylinders which 
were rebuilt last year when a new pump was installed.         Pretty 
sure it is sometning wrong in the control unit but don't have a clue 
what to look for.   Can you help?   Thanks,    John   (NE Oregon)

                    In the wide-open spaces of NE Oregon