cheers guys it looks like both the IRD & VCU. Went to the main dealers and they are asking A$2100 for the IRD and A$3700 for the VCU. I don't know why the VCU is so exy unless it comes complete with the drive shafts?
anyway I have removed them both and found the problem with the IRD. The two Taper roller bearings holding the crownwheel in place are worn. there is a bit of damage on the two gears but nothing to worry too much about i'm going to replace all the bearings & seals in the box and see how it goes. not looked at the VCU yet but don't know if I should be able to spin half the shaft at a time by hand or does it require some torque anybody know??