[AT] Compact JD 650 tractor question

[Charlie V]

My s/son has a 1984-1986 compact JD 650 tractor.  As I understand it,
it has lately developed a problem with the power steering.  When
turning to left, steering works normally.  When turning to right,
serious arm power is required to make it happen.  I can come up with a
couple of speculations as to cause for this condition, but suspect
someone on the list may have been through this problem and can  advise
most likely problem and fix.

Thanks for any help you can offer.

Charlie V. in WNY