Are you talking about a REAL BMW Dealership? Or a dealership that just sells any car on mass?
Take the oil cap off when the engine is running and see how much oil is sprayed, make sure you have a TYVEK suit on and some goggles cause if I am wrong and “The Dealership” is right then, I have learnt something else (but every day I am learning that I do not know nearly as much as I should do!)
They have told me it needs a new oil cap, but it won't be covered by the warranty so I will need to pay for it.
I've asked them to let me know where in the terms and conditions it says oil caps are not covered by the comprehensive £0 excess warranty that also includes wear and tear.
Once they agree to pay for it, I will let them change it, so that I can bring it back a couple of weeks later to have another go at working out what the problem is, when it is still leaking oil.
Honest to god its such hard work getting them to fix the actual problem on the first 3-4 visits.
This is why I wanted to know what it was before I went into the dealership, so I could google it and research it myself (obviously something dealerships can't do) - and your original suggestion checks out as probably what is actually wrong
I'm not going to take you up on your suggestion to remove the cap though, that would be fine under normal circumstances, but if the PCV is actually faulty, or there is a fault in that engine bank causing massive blow-by then it's going to spray out its oil (had that happen on a Peugeot many years ago with bad piston rings) 🤣😂