Finally got my Patrol back yesterday
Quick update:
Oil - They used about 12l to fill the box and the torque converter. It was completely drained of all the old oil. Unfortunately the oil was mixed with other old oil when drained and could not test it.
The 2 most probable causes for premature seal failure according to the mechanic is excessive Heat and the wrong oil (which could also lead to excessive heat). Both causes have been excluded as all the other seals was in perfect condition. even the outer seal on the reverse piston was still in perfect condition. its only the inner seal that perished. The only conclusion is that it was a bad part from the beginning. Tough luck i guess.
For now im happy that i have my Patrol back

and that my box is working again. I need to take it back for a followup inspection after 1,000km. Also got a 12 month / 10,000km warranty.