Where are my default planes?

Since installing FSX, I have noticed that there are some of the "included" planes that don't show up (and never have showed up) in my library when I load Free Flight (or multiplayer). For example, I have never seen the Maule or the Grumman Goose.

I HAVE looked in the Sim Objects\Airplanes folder, and those aircraft are in there--but they don't display in the game and don't seem to be available to me. Is there anything that I can do to get these original planes to show up in my library?

Re-installing FSX is my absolute LAST resort, so any ideas aside from that are much appreciated. I have a handful of addon aircraft in my library, but that's not really a big deal if I do need to reinstall FSX. I have a backup folder of all my addons so I can recover them later in neccessary. I'd love to avoid that scenario if possible.

Thanks for your time. 🙂