i do recall recirc valves being shitty on the 1.9pds but cant really diagnosis over the web,
if you can get a known good unit might be worth swapping and trying
If your Z is a VLSD either JDM or UK then this is a direct fit, if you have a JDM open diff then we can supply a different LSD
Winner then erm I'm in Blackpool till end of week and can't pay till then