This isn't the most active X3 forum, hence the relative silence *chirp, chirp*

The 2004 model year had a stiffer ride, so given that you are up north, even the standard model might ride a bit firm for average tastes.

Problem areas are minor. They include creaking/noisy window frame guides and possibly some clattering from the moonroof. The moonroof itself may be prone to some problems where it gets stuck in the tilt position or one pane does not work. The moonroof drains (from the frame to points near the wheelwells) must be clear or else clogged drains can mean wet carpets.

The transfer case is a minor weak point. It is advisable to have the fluid changed at 100.000km or earliest opportunity. Mixed tires (brands, treads designs, and tread depths) can have a detrimental effect on the transfer case, leading to premature failure and a costly repair.

The wheel bearings can crack or deteriorate over time, so check for any rumbling or whirring noises while driving and/or turning.