variations of the rebuild in the thousandths to ten-thousandths of an inch in difference.
I know that sometimes when the stock turbos expire, they will catastrophically destruct - so much in fact that the center cartridges have to be replaced with new units. It would seem to me that these sub-par Sport500s are likely tied to the machining done on a used, rebuildable cartridge whereas the good Sport500s that dont have this issue were likely rebuilt with a new center housing.