From my dealer experience, CPO (or dealer) has covered replacement if it appears the materials were not up to standard. I have had various trim pieces, ranging from window switches to gear sticks, replaced before.
Strangely, the piece I'm referring to does not appear to be on that parts list you posted. Although it appears every other piece of the tailgate is there. The piece I'm talking about bridges the gap between the bed and the tailgate, when it is lowered. And it didnt start cracking until I had the truck for at least 4 months. Simply lowering the tailgate would cause the hinges to crack. That's why I'm curious to see if this has happened other owners.
