hmm, I don't know about differences in quality. Two months after I bought the car (I bought it second-hand, since I refuse to pay so much money for a car) the a butterfly valve got loose in the inlet manifold resulting in major engine damage!! Cost: 3500 Euros!!! When I asked BMW for lenience, they refused and said that such damage could be considered 'normal wear and tear' in a 9-year-old car with 200th kms!! I was flabbergasted: first of all, no object should be able to get loose and fly in the engine, and definitely in such an expensive car, second, I found many reports of this problem on the internet, so it's a consistent problem, third, they redesigned this manifold from 2005 on suggesting they knew about the problem. So, I don't have such a high opinion of BMW-quality. (In contrast to Volvo, as I had done 544th kms with a 1998 V70 TDI, and I never had such a major cost as with our Siebener...)
Do you really believe build quality differs so much between a european and american version of BMW? I almost can't imagine BMW would use different build material in Europe than in USA, or am I wrong?
Anyway, I hope yóu'll solve your problem quickly, because it must be an annoying one...