1. Well, you know this...the transmission will most likely have to come out, whether it be for repairing it, or a swap.

2. Most likely the problem is inside; opening it up= relatively big $$

3. In terms of major component reliability, BMW's drivetrain has never been a strong point, so you don't know what lies ahead with this transmission even if you fix this problem.

4. I don't think you can actually get that specific auto trans parts from BMW. I bet cores get sent back to BMW NA, or even France. Here's as specific of parts you can get otc: http://realoem.com/bmw/showparts.do?...38&hg=24&fg=15

It looks like, you'd be better off getting a low milege transmission Bavarian recycling and save yourself potential headache down the road. Just for good measure at this point, there'd be no harm in swapping tcu or any other appropriate/easily accesbile relevant control unit to make sure it's not a fault there. I'm sure a fellow 3.0i owner in your area would be willing to help out..