One thousand kilometres in one day? That's amazing!
As far as I know, Pajero reduces oil only because of turbo. There must be play in the turbo or the seals must be worn out. Turbo rebuild kits are available abroad, but I haven't seen any locally. I think you should consider replacing the turbo. Make sure you get a working turbo preferably from a nose cut.
How do you know half the oil was consumed? If the level is exactly between top and low, it takes hardly a litre of oil in 4D56 to top up. Should be similar in 4M40.