Transfer case, you can take care of with an expensive fluid change. Valve cover gasket is a DIY if youre so inclined. Oil filter housing gasket is easily fixable on the N52, Vanos valves and their seals are also an easy fix, automatic transmission fluid change is a must along with servicing both differentials, oh, dont forget that coolant flush because the electronic water pump is over 350.00 for just the part......but these cars are reliable!
seriously, Ive had mine for just a couple of months and have had to do a LOT of servicing.....but the car has over 100,000 miles and drives like its brand new. the motor is very strong and smooth, smooth, smooth.....the interior is holding up great, the doors shut easily and quietly, the wipers operate without a sound, the suspension is crisp and predictable, so I have to say I love BMW's philosophy and approach to car building.
Are they expensive to maintain....yes. do you have to keep on top of them all the time...yes. For me, I do it because I want the car to keep performing and feeling exactly as it does right now...which is amazing. My dodge pick up on the other hand is another story!...I love the truck...but I dont fuss over it.....I change the oil and keep it maintained...but I dont worry about it......The Bimmer on the other hand.....