I'm on a similar boat as you. you are not alone. I had SES light for injector. Dealer changed injector and SES light came back. After back and forth by dealership and BMW NA, they decided to replace the computer. SES light is no longer on and all monitors are finally ready. I still don't have my car back as it needs Approval by BMW NA before release by the dealership. It's been 3+ weeks.
They also said it does not look like carbon build up related...
All emissions components by law is supposed to be 75k (I think). So BMW needs to take care of this, as long as it can be traced to an emissions related issue.