I bought a micro filter from them:
Around $50.00 delivered, a few minutes to install and very easy to reset the iDrive/dash display for a further 2 years. Your service guy should be ashamed of himself as this is one of the EASIEST jobs on an E90.
By the way, my dealer's parts department wanted $150 for the filter, then $100.00 because I told him that the sales guy I have dealt with insisted on trade price for me. Still double the price!!!! Never from a dealer unless it is warranty
328i M-Sport, Estoril Blue, Carbon XP 35 Tint, front heated seats, black Dakota, Sports Suspension, Anthracite Headliner, HUD, Pro Nav, Sunroof, hk 600w, Bi-Xenon, 19" 403M wheels, Reversing Camera, DAB+, Xenon, BT Ext Connect. JB4 on Map 2 with Catless DP produces awesome performance in Sport.