Like everyone has stated before, it will probably be a heck of a lot cheaper and a much better idea to just sell your 6MT and buy a new or slightly used DCT M3. There is no way a local BMW shop or any other shop will have as high quality work as what the car comes from the factory. Does this not make any sense to you?
2012 Audi R8 V10, 6MT, Suzuka Gray, Larini Clubsport exhaust, Klassen M52R, GMG springs, Satin Black badges
2012 Audi A6 3.0T Prestige, Moonlight Blue
2014 BMW 528i, Space Gray
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