WHat am I missing?

Remove two screws at bottom of seat back.
Pry out rubber plug and remove screw holding lumbar support lever on seat side.
Wiggle / pry two headrest posts from black plastic holder at their bottom end ( This carriage raises and lowers headrest).
Disconnect wire to headrest at yellow connector (neck-pro power).
Pull up on headrest.

It comes to a solid stop once the bottom of the posts enter the guide.
There is no release button, that I can see/feel, as there was on the 210 front seat.

WHat is the last step in releasing the headrest?

Remove two screws at bottom of seat back.
Pry out rubber plug and remove screw holding lumbar support lever on seat side.
Wiggle / pry two headrest posts from black plastic holder at their bottom end ( This carriage raises and lowers headrest).
Disconnect wire to headrest at yellow connector (neck-pro power).
Pull up on headrest.

It comes to a solid stop once the bottom of the posts enter the guide.
Sitting in the rear seats, now peel the upper MB-Tex /leather up and forward a few inches (there are three u-shaped plastic long clips that secure the after edge of the Tex to the seat frame; push forward and they will come off) and you will see a steel clip that has engaged the headrest post. Release some clip pressure and out comes the headrest.