LCI levelers emergency retract warning.

Over the course of 4 years, the emergency retract warning on our levelers has gone off a couple times when driving but went away. Now it seems to have become constant. Anyone have a troubleshooting technique for identifying the culprit? Watching the jacks while this occurs (RV parked, running, in gear) shows no visible movement. All the retract pressure has to do is fall below about 2K lbs of pressure and the pump will start to build it back up. With no external leaks, it doesn't take much internal leakage to trigger the system. With the problem being either one of four jacks or the power unit, how does one isolate the problem without just throwing parts at it?