Morning Claire
I agree with John, I would be suspicious of the Dealer. There is a BMW Specialist Register (Google is your friend) take a look and find one near you.
A "Drive Train" warning can be triggered by many things other than the drive train. You don't say which model or engine but if petrol Coil Packs and or Spark plugs are known to fail and will trigger the warning. As will fuel pump issues (petrol and diesel), low oil levels (engine and/or gearbox) low coolant level causing over heating.
So as John says talk to a BMW Specialist they will have the experience and knowledge to offer constructive advice
Dave