OnGUI() not being called in Monobehaviour

I've got two cameras, and the OnGUI() isn't being called in both of them. I tried using the working OnGUI to send a message to the second camera to call it's OnGUI but I get the error that there is no receiver.

CameraControls.cs (main camera)

     //caled once per frame
     void OnGUI(){
 
         Debug.Log ("CameraControls.OnGUI() called.");
 
         //call the OnGUI() for the PlayerInventory that sets up the quickbar contents
         Transform cameraChild = transform.Find ("InventoryCamera");
         cameraChild.gameObject.SendMessage ("OnGUI");
     }

PlayerInventory.cs (child of main camera)

     //used for GUI
     void OnGUI(){
 
         Debug.Log ("PlayerInventory.OnGUI() called.");
                 //other code, but the above is not printing
         }

I know this looks unorthodox, but Unity isn't calling PlayerInventory.OnGUI() automatically. It does have a GUILayer component. I've also tried renaming the OnGUI function for this setup with the same results, even though I successfully call other functions from PlayerInventory.cs with this script.