Just another thing – driving round in 4wd for the last month won’t have done it any good at all.
Exactly that. 4WD when in snow or mud but back to 2WD when you get on the road. The Navara is NOT permanent 4WD and does not have fancy diffs to take care of it. You can permanently damage your drivetrain by leaving it in 4WD in ordinary conditions, and it will not be covered by warranty because the instructions specifically say that you must not.
The flashing light shows it’s gone into 2WD mode but the axles are still wound up. Try reversing it, or even better take it onto a slippery surface and spin the wheels a bit in 2WD mode. If you are lucky you will not have permanently screwed it.
And BTW we have had a Navara for the past 4 years