I have a 99 model petrol its same as 4.2L in regards to rear axle seal..Its more than likely the inner rear seal has gone, not he outer grease gearing...peice of piss to change, but get the geuine seal, it seals better than most aftermaket seals. I did one on my patrol a few months ago, just have to be careful when putting the axle in you dont put to much weight on the seal as you slide the axle back in. Might have to repack the bearing as it would of washed out the grease from the bearing.