Hey Perry,
First thing – check to see if the Press a Button action can press the checkmark button.
I'm doubtful, but this has worked before in cases where I didn't think it would.
If that works then you’ve got the Button condition for an IF/THEN.
If that doesn't work then run this macro with the given window frontmost.
Front Window Analysis Tool Using AppleScript System Events (List UI Elements)
Post the result. Zip a text file if necessary.
This will tell us how much AppleScript UI-Scripting can see of that window.
-Chris