[Ken Maltby]

The "inner" black plastic has no parts, that can fail. It is a solid piece of IR transmissive plastic, shaped so that it can direct the IR emitted, on the edge of the PCB, through the scalloped part then bounce on the corner, to send it through the plastic to the internal edge and then across the gap to go on to the scallops the opposite side where it gets bounced into the IR receivers on that side of the PCB.

If something obstructs that path the touchscreen can stop working. If the parts are not aligned properly, the touchscreen can stop working.

I once spray painted the bezel of my AuraHD and got some residue on the black plastic, it was only after repeated cleaning was I able to get the touchscreen back working.

Luck;
Ken