Navara D22 front Diff

Hi,
We have just returned from the Simpson Desert and had a mate of mine travelling with us in his 3 litre D22. A short distance into the French line (heading east) he was coming up a dune and there was an ugly bang, then clunk...clunk.... After spending some time trying a few different things (ie. hubs locked - unlocked - 2wd - 4wd etc and then jacking it up - spinning wheels, pulling the hub apart and so on) we diagnosed that the diff had let go. He has not had it checked yet by a mechanic but in the meantime we were wondering if anyone else has had anything similar happen ? Is the front diff in a D22 a weak point ? (I guess you could say it is in most 4wd's) and if so do you think a front locker would help ?
I look forward to your comments.

By the way, he continued on in 2wd and only needed snatching over the crest of a handful of dunes and a winch up Big Red when he ceased to proceed. Fortunately the navara was one of the lightest in our group and one of the few with freewheeling front hubs so continuing on in 2wd was no real problem.