Is the Gearbox Drain Plug on a 2004 2.8 JTD Ducato the one on the bottom of the diff housing that has an internal square drive in it?
Many Thanks

That is the correct drain plug, the original quantity was 2.0litres but has been revised to 2.7 so as to allow better lubrication of the fifth gear that is outside the main case.
It is good idea to use the original oil as jreplacement Tutela SAE 75W-85 APIGL4
Cheers