NOTE: The gearbox serial number is on top of the gearbox.  Look down in front of the throttle body, between the rubber intake duct and the PCV preheat hose.  Picture.  I think the later slave cylinder use started in 94, but I am not sure.  UPDATE: The slave cylinder on the left is definitely the 94 and later style.  You have some chance of determining clutch disc wear with the earlier version, but no chance with the later version.