The fuel pumps die constantly, the injectors fail, the diverter valves flutter and ware, and the turbo's will die (not sure why though). If you like to DIY the fuel pump and injectors can be done without lifting the car but the rest do. Also these parts can be very expensive. I don't have a 335, but I do know there are several cars out there with very little problems and some cars with constant problems. Luck of the draw I guess. Go to
www.getbmwparts.com and check out prices for parts. Or you can do some searching on the aftermarket side and see what's available to replace some of the weak stock parts.