LOL, I bought the die directly from RCBS and have talked to Rick several times!

Have you "mic'd" the pin bushing, to be sure that it is a problem, or is this just an "eyeballed" measurement? Just curious.
I mic'd it and tried a case in it. Factory Lapua brass measures 2.897 . . . with bullet installed it measured 2.900, all very close!

Instructions state: The Decap Rod assembly comes with an expander Ball/Decap Pin holder installed to allow for the proper preparation of a new lot of brass. The Decap Pin holder "FOUND" in the accessory bag "MUST" replace the expander ball for proper use with the neck bushings!

These instructions seem pretty straight forward to me! Again, the accessory bag was not in the case! I could use the sizer like it is, but I want to use it the way it was designed to use.

I wish the instructions for this part were a little more detailed, but trial and error will get the job done.

I really don't understand why you need one expander ball for new brass and one for fired brass!