I don't understand what they mean by broken. If the motor worked fine, as you say, they may be referring to the mounting or housing of it being broken. I would go in to see them, with a mechanically inclined friend if I wasn't familiar with this myself, and ask them to show me what is wrong. Level head is always good. Just ask them to help you understand what is wrong. And wait to see what BMW says or the dealer proposes themselves to resolve the situation.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue