Case International 235 Compact tractor hydrostatic lever issue

[atibrad]

I believe my tractor is a mid eighties model. They havent made them in years. It used to operate very well until a few months ago I was getting ready for seeding my lawn and was disking it up when I noticed the hydrostat lever (forward and reverse) became really hard to move forward or backward. It only did it occasionally at first but now its all the time. Checked out the linkages from the lever itself down to where it goes into the casing and there isnt any obstructions. Anything I can do? its a 3 cylinder Mitsubishi diesel engine if that makes any difference.