"F" Button in Shape Key Editor Not Showing Up - Why Not? I'm trying to export a model with armature and shape key animations. I've been following this tutorial: 

https://www.youtube.com/watch?v=wvjwTnS6vhA

This process works fine for the beak of my character, but not for the eye lids and pupils. The pupils have shape keys to make the character look left and right.



Now I wonder if it's because the beak only has one shape key and the eyes and eyelids have multiple. But so far, the beak is the only one ready to go.

I just need the animations to export into Unity with the shapekeys. Here's my .blend file:
The "F" button is to tell Blender to save a data block even if it has no user, so it appears only when... you have a data block!



In your picture, you have this situation for that eye:



the " + new " button means, there's no data block, and you can add one (an action in that case). Then, the "F" button will appear.

edit

I think that eye has something different than the other...



selecting that green NLA editor stripe, and using TAB it expands, and the " + add " becomes usable, but acts weirdly, at least...



I'm not an expert though, and can't understand how to fix it. But maybe you know what happened to that strip?