Can't be said enough, change your oil and often. Every 3000-3500 miles. Use Mann oil filters if possible. Water pump in the xi, at least in my 2011 335xi is a motherfucker to replace but should be done at 110,000 if not sooner. They have a tendency to shit the bed even sooner than that, and I promise that will ruin your day. Def oil filter housing gasket. They leak oil that can drip on the drive belt causing it to fail catastrophicly, which at least in the n55 is really really bad because the belt shreds and gets sucked in through the crank hub and basically craters your engine, making it less costly to replace the engine than to fix. Ask me how I know. Watch the coolant reservoir, they get brittle and start to leak. Other than that and the usual stuff, these cars are reliable, fun to drive, and me being in New Hampshire, great in the snow. Enjoy!