[C. Ludwig]

There is supposed to be a slight difference in the gear that makes the 8 more suitable for high revs, but they're interchangeable. The whole 8 gear/bearing isn't a whole lot more than the bearing itself. Even closer in price once you factor in having someone press the bearing for you and how many they'll possibly screw up.

The oil passages of the 8 gear do not properly line up with the 7 irons. A little work with a die grinder fixes that issue.