I worked on this just a couple weeks ago and already forgot some details, but I do recall running the #21 bit through this assembly. That roll pin is borderline too long, so I filed down the ends a bit before assembly so it didn't bind in the plastic housing. Used the vice to press the pin into the gear and shaft. The assembly of the door mechanism requires a lot of filing and cleaning up parts in order to get everything working smooth.
One hint, something I wish I had done but didn't, when you press the other roll pin in on that shaft, the one that falls into the slot to lock the door shut, is to make sure the seam on the roll pin faces inward, or away from the slot. My seam faces the metal bearing surface, and as it falls into the slot it catches just a little bit, so I get a "ker-clunk" instead of a "clunk". Not a big deal though.