What can I expect from a repair cost over the next three years?

What is the repair cost of the carbon issue? I am contemplating extending the warranty for 3 years for fear of that very issue.

FYI... most extended warranties do NOT cover the carbon issue. They consider it outside influence not a defect. Most extended warranties only pay for the replacement of a failed covered component. Since there is not a failed part there usually is no coverage to clean carbon build up. I think BMW's ESC (Extended Service Contract) and CPO warranty do cover carbon cleaning. It's a hefty $1000+ repair as the intake manifold has to be removed to perform this operation. I would talk to a BMW service advisor. BMW has several levels of the ESC warranty. I want to say it's Powertrain, Silver and Platinum levels. You'll want to ask the BMW advisor if the ESC covers carbon build up and make sure you buy the appropriate level if so. The main differences between the different levels. The lowest covers engine and transmission. The next level adds is basic electronics and body mechanical like window regulators and door lock actuators. And the higher end adds in Audio Systems, Nav Systems and related components. Do not ask the sales or finance staff what is covered. Make sure you go to service to ask the advisors or the service manager. Let them know what you're trying to accomplish.

Thanks