No idea how it happened and ive had the truck for about 18 months, only reason i have changed the oil was cos i put the lokka in the front and thought i would do all driveline oils at once, have only done 1000ks in the time i have owned it as i have a work vehicle, the oil was clean when i bought it and i reckon i have done about 50ks of hard 4x4, some sand and the rest highway. So im not sure what has happened. And as i said it still drives fine and no noises from it?