Hi Mark,
The wear will occur in the inner 24 spline of the drive flanges at the hub. It's pretty soft material compared to the hardened differential and axle components. Probably should have been clearer about that. I always carry a couple of spares.
If you are taking the whole assembly out of the vehicle for overhaul you can check it for straightness yourself. Take the hubs, stub axles and backing plates off, make sure you don't mix them side to side when you reassemble - important. Get an assistant to hold a staightedge or clamp it across the end of the casing so it has the same overhang on each side. Now hold or clamp a similar straightedge across the other end of the casing and accurately measure the distance between the straightedges on either end. Keep a note of the measurements. Now move the two straightedges to different locations around the casing (say 12, 3, 6, 9 o'clock) and compare the measurements. The distance out from the axle centre accentuates any bend in the casing and it should be apparent.
No bend should be no problem!
Bob

