I hate these kinds of posts too. Its how incompetent dealer/techs abuse customers. Most simply bend over.

You have two issues:

The first is a misdiagnosis and charge for the wrong reason

The second is you did repairs that should have been paid by the CPO.

What did the service manager say? Not the SA (adviser), but his boss. When you went back and said 'what are you going to do about this?'...Not real confrontational, but low key- just say I know stuff can be hard to diagnose, but lets all be adults and be honest here....The problem is that this is really hard to prove and to convince them...and then, how will they get the money to you? Transactionally it is almost impossible, and they are so busy and stretched it will be easier to deny you.

Under a CPO the work order will come in and once the tech said "hose" the clerk in the back didn't bother submitting to BMWNA- they said you pay.

Now they'd need to explain all this to BMW outside of the work order/paperwork/automated submission process. And they'd need to accept at face value the fact that their tech was wrong and yours was right....and that nobody fixed the hose, tightened the clamp, etc, etc.

But I do think that you have a claim for the first part- if you paid with a credit card, you could charge it back and battle the dealer for the $150.

Now, what about the 'real' repair? I seem to recall the CPO requires the repair be done by BMW (under the warranty they cannot require this, but a CPO they can- read your CPO plan). Since you didnt let them do it, they may deny it and win. Even if they misdiagnosed it.