How to select/list all users of an Action? I have a (comparably) complicated, non-humanoid character rig. I am having a lot of trouble exporting this thing to Unity, so I am trying to clean it up without ruining all the animations I made (for the second time). I have one Action that has 3 users, but I only have 2 armatures; No meshes need to be linked to the action because I am using shape key driver-bones to do those deformations.

I have looked through all meshes for this character, selecting the Action and pressing the "x" button, but it is not clearing a link to a user--I can't figure out WHAT extra object is the 3rd, superfluous link to this action! I need to remove that link.

How can I get a list of objects that are linked to this action? Or select them? I do not remember how to use Python scripts in Blender but am open to it.
Any animation editor will show you such a list, provided the keyframed objects are selected at the moment. If you don't know which specific object contains the action you want unlinked, you can simply select everything in your scene, with a, and then check an animation editor. All keyframed objects, and ONLY keyframed objects, will be revealed in the animation editor in question. This list will show both the name of all keyframed objects, as well as the actions to which they are associated. Below, I show the view from the Dope Sheet, but it also works with the Graph Editor.