I tend to agree with them, valve cover gaskets have nothing to do with a coolant leak. Head gasket, valley pan gasket maybe, but strictly speaking what is wrong here is your dealer is trying to fix something that has nothing to do with with your leak.

I suspect what is going on is the dealer has miscommunicated what they are actually going to do. No dealer certified mechanic (even a BMW one) is that stupid.

(Edit: Oop you said 3.0. No valley pan gasket.)