As I said I only tested it on Titan. What you can do is to run the script, open up window spy and hold your mouse over the checkmarked autopost checkbox. On titan for example the "check" is white-ish while the background is blue. Hold the mouse over the check and see what colour it is (window spy will tell you), now just replace the 0xFFFFFB with what ever colour you get. Also change the coordinates while you are at it to the same point on the screen (window spy will also tell you that). The colour I used to check the check box might be diffrent also on your skin (as well as pos), as long as the colour is not the same as the background it will work.
Here I show you (the red arrow represent the mouse pointer, could not capture it):
