IRD & G/BOX OIL change TD4

Hello all.
I'm looking to find out at what point do you change the oil in these units, and are they done at the same milage? I gather that the G/box for the TD4 is the Getrag unit, but is the IRD the same unit for all?

There seems to be nothing regarding the final drive and an oil change in the Haynes, so take it this is a sealed unit.

Any help and advice welcome on the transmission service side.

TD4 2003 manual gearbox.

Cheers all.

personally i do the yearly for most people on average mileage

Hi,manual gearbox 96,000 miles or 8 years via the Haynes manual, recently changed the oil in my IRD and final drive. The final drive has no drain plug the oil can be changed by removing the filler/level plug and either using a large syringe or as I did by syphoning it out !