Those industrial subplate valves are available everywhere, you can take that one to just about any hydraulic outfit and get a new one in any of several different brands, or find a vickers vendor, get a seal kit and pull it down for inspection and cleaning. Check to see if it has manual override pins on the ends, sometimes they get stuck. Have had a couple that were intermittent just because somebody tightened the nut holding the coil on a bit too much, go figure.