JCB Sitemaster Backhoe suddenly stopped going in reverse

Hi, I have an 1990 JCB Sitemaster 4wd with a Syncro Shuttle transmission. The other day I was backing up a small hill when it seemed to drop out of gear. I put it in forward and it works fine. No reverse. Here is what I have tried so far: Removed the F/R solenoid valve. When switched from foreward to reverse I can see the valve shaft moving back and forth. I dissasembled the coils from the valve body and reversed them and they still actuate the valve shaft. The coils ohm out the same (~5homs) and both draw the same amperage. I reassembled and still no joy. Recently (a week before this happened) the hose to the cooler popped off and drained a couple of gallons of fluid. I topped it up and replaced the filter. I have not checked the screen at the bottom of the sump yet. Any ideas? A couple of simple questions: What fluid is equivalent to JCB brake fluid? Thanks, Chris Backhoe Info: mach-s/n: SMBT4010/354682/7 eng: AC532616T fnt ax: 03633 rr ax: 03400 gearßx 445/164/6/00585