As someone who's had to fight BMW to honor a warranty repair (and won) after a FSE had come out to "inspect" my old modded E46M3 let let me give you my $0.01.
Going to another dealership is pointless. As pointed out earlier, warranty repairs are paid for by BMW. For high priced repairs BMW will send out a FSE to make sure the dealership isn't trying to rip them off. Regardless of what caused it, the FSE (and therefore BMW NA) has placed the burden of proof on you to prove them wrong. Even if you go to another dealership and find a SA that agrees with your assesement, someone has to foot the bill. I don't think the dealership will step up to bat unless you know the owner and he owes you 6k..
In my situation I had taken the car in a few times before for the problem and they failed to repair the car. I was able to arbitrate through the BBB because BMW NA has an arbitration clause for my state. It looks like they have it for MD also so you may want to investigate it. Note: BMW will have a representative (not the FSE) take the case, and you get a 3rd party to listen to both sides. If I remember correctly, you can choose to meet in person, via phone, or do written statements. It does take time however, and if the decision is found in your favor it's legally binding to BMW. If you loose you case, you can always attempt it again in court.
Another option you may want to consider is calling BMW NA Customer relations and bitching - a lot. To be honest though, most likely the CR rep won't assist you since they are just note takers/read off a script and have no authority. If you complain enough though, you might get someone in the NJ office to call you back. They may be willing to work with you and work out a semi-goodwill repair. That's what happened with me, but once I started the arbitration process with the BBB, the BMW NA rep in NJ decided that he didn't want to deal with me.
You could also laywer up, but since this doesn't sound like a typical lemon law case since you didn't take it in before for the problem (or it was not mentioned). It might take a few more calls to get a lawyer to take it but I suppose it's possbile.
Good luck with your situation. It totally blows and I've been in your shoes. If you have any questions about the process I went through, PM me and I can go into more detail.