I had my cylinder head replaced after the lifter replacement didn't work. Fortunately my dealer was very easy to work with.
If your dealer is giving you a hard time, demand to talk to the general manager. Prepare a written narrative of the chronology of events and hand it to him. Also mail it to the dealership certified mail today (so it can be delivered by mail tomorrow, the last day of your CPO). Also copy BMW North America on the narrative.
All of that is to establish a paper trail showing you attempted to get what you were entitled to under your CPO warranty in case they won't cooperate with you.