About one month ago I had the same problems with carbon buildup and injectors with my 2009 335d with 46k miles. First I was told that it was carbon buildup that turned the SES light. Then I was told that the injectors were leaking. After all was said and done, the dealership ended up replacing the cylinder head, all six injectors, intake and outtake valves and the fuel injector pressure sensor.
Everything was covered under warranty so I didn't have to pay.
I think that these problems will come back in about 40k miles, but I have the CPO warranty until 100k. Once the warranty is done, I will start using diesel additives with cetane boost.