Last week, or week before last on Muscle car or was Trucks on spike tv that showed how to rebuild the rearend.
What I did see when the put the paint on the big gear(the whole width of the gear about 4 inches long), and spun the pinion until the painted section had came back around. If the area were there is no paint is the area that tells you where the gear is going to be wearing.
If it is to the outer edge or the inner edge, then you need to rehim, or take out a shim for the pinion to correct the problem. You want the wear directly in the middle of the gear, this is dead on.
I hope this helps.
David