This has come loose, and it causes the trigger/button to rattle when I go over bumps. I know this is what causes it because when I squeeze it together, it does not rattle. Is there a fix for this, or will I have to get a whole new ****? Left side piece of leather

 

Super glue.
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You don't need to super glue it; just get the two replacement leather halves.

I just did this to my 2014 King Ranch, but it was for the leather wearing, not because of this.

The two side leather pieces basically snap into the main shifter body, using small L-shaped plastic hooks. It's likely that one of your hooks has broken, allowing the side piece to become lose.

It takes about 10 minutes to replace them, and cost me ~$30 off amazon to get replacements.

If you go this route, use a flat head to pry way from the front/trigger side of the shifter.

 

If you decide to use adhesive, super glue may work but if you use it and it fails then I would use an epoxy.

 

The dealership wants about $40 per side... I think I can live with it for a while. To be honest, I am not sure that would fix the rattle anyways.