The lemon law is a bit of a grey area. It differs from state to state, but the basis is the same. If you take your car in for the same problem X number of times (each state is different for the number of times I believe) and the dealer can not fix the problem it will be classed as a lemon. Now if you have a badly make car that keeps going in for different things that brake or need fixing the car is NOT a lemon. Obviously your SLIPtronic is a major problem and you need to find out the number of times you have to be in there in your state before it is a lemon. The dealer should be helpful because it is not them that a buying the car back it is BMW.
Good luck, keep us informed.
Good luck, keep us informed.