[mpj76]

Test drive went well. Its pretty ingenious how that thing works. For others' reference, to insert the missing planetary gear, the retaining bar has to be all the way out. Spin the unit so that the other small planetary gear tries to crawl out also. It will move towards the open area of the carrier. Get it as far out as possible without actually letting it drop out. If you let it drop out, the other two gears (the ones that the axles go into) will also fall out, creating a mess. With the small gear almost out, insert the other gear through the OPPOSITE opening. Then twist the unit the other way so that the small gear moves back where its supposed to be. Both gears will move together into their respective resting areas. Now the pin should be replaced. If the holes don't line up, back the gears out again and retry on other cogs until they're "In time" with each other like Jester said.