These are the main ones that come to mind:
- Standard N55 stuff like Valve Cover Gasket (VCG), Oil Filter Housing Gasket (OFHG), and oil pan leaks. If you see oil on the serpentine belt...take care of the OFHG.
- Cracked valve cover
- Cracked or ruptured charge pipe
- Radiator leak by the plastic bits
- Rod bearings?
- Carbon build-up on the intake valves
There also the usual BMW cooling system maintenance but that's not unique to the N55, nor is what aeems like an eventual clip breaking on the moonroof cover.
I won't jinx anything but will say that I've got 10yrs with my 2014. About to replace most of the suspension but mainly since I know one of the control arm bushings is bad (missing a chunk out of it) and figure...'while I'm in there and in need of an alignment...'. Should give you a hint as to my position on this underappreciated beast if I'm willing to voluntarily make that investment.