If you somehow managed to get everything aligned perfect great, but 9 times out of ten this will not be the case. If so fallowing will allow you to line up problem parts hopefully without re-opening the gearbox.

Use your small thin tools to re-position problem parts if possible.

First with the gearbox held together by hand, check for proper wire and safety-latch placement.

Then try to make sure you have the spring guide in place. If so then you can keep holding the two haves together.

At this point check to see if the gear and anti reversal-latch axles are placed in the bearing, if not you can manipulate the position of these parts with a small thin tool. If the anti-reversal latch is too far out of position you might have to take the gearbox apart again and retry step 3 and 4.

If all the parts covered so far look like they are in position but the gearbox is still slightly cracked open it is most likely the piston. Luckily there is a trick to dealing with this. Which will be step 6.