Clocking gears: I took a look at the Nexus-8 service manual. So it appears, that there are two sets of planet gears there, side-by-side, of different diameters and number of teeth. When the gears are clocked, the clocked tooth of both gears line up perfectly. I do not know if those gears are two separate parts, or as a unit. But either way, my guess is clocking them that way may prevent some gears from fighting each other in zero backlash or some other way. If they point out in the service manual to clock the gears, there's probably a really good reason for it.