Specifically, want to know how the head rest retainers stay in place. Looking to add a third headrest to my seat, and before I start disassembling the thing... would like to see if anyone else has done this. Ive found a source on the actual retainer which installs through the top of the seat... I just dont know if there is a second part that woudl be needed to secure it into the seat itself (so this retainer grommet doesn't pop out basically). I assume I will need to reinforce the area where I cut and add in for this third headrest, but its just theoretical right now. Want to get all parts first. Thanks

 

The seat in question.