Is there any way of telling the age of a transmission, Marks adapters website states 'Nissan updated all GU Patrols as of 08/2004 with a longer spline main shaft and 5th gear'. Is this what that modification is trying to achieve? Although mine now has a 4.2 box in it, how would I know if the box has the new spline. My rpm at 100 sits at about 21-2200 so it probably hasn't got it.