I would think that if you are going to open up the transfer case anyway, might as well replace the output spline while you are there?

As I understand the longer shafts are for an alternative repair method to avoid having to replace the transfer case output spline.

Also IIRC, there is no inherent weakness in the mentioned parts, sometimes a combination of factors causes the AC evaporator condensate line output to fall directly on the spline area which causes corrosion and weakens them enough to fail. So the long term fix is to inspect the AC drip line and make sure it is properly positioned.

__________________
04 X5 3.0i auto
03 X5 4.6is