Dealership replaced five of the six injectors on my car under warranty at about 42K miles. I also have an 09'. So there's definitely something with some of the injectors that makes them go bad. So I'd probably start with the injector(s).
09 E90 BSM|Injen DCI|ER Charge Pipe|AR Downpipes|AMS Intercooler|Cobb V3|BMW PE