have you checked to see what condition the hydraulic fluid is in? do you know if any of the filters have been changed? From memory these filters are kind of buried up under the floor boards and somewhat difficult to access.
st thing to do is check hyd level then change hyd filters which are cheap from JD and check/clean sump screen(key 26). Then check hyd stand-by pressure. 2 ea-AR75603 Filter Element - ELEMENT,OIL FILTER ADD 8.31 USD 16.62 USD