I hear in some of the discussions on this site about carbon buildup especially with the turbo S models. Is there a way to do any preventative maintenance to prevent or delay this issue? Does the quality of gas help, say adding a Premium (93 octane) vs Special (89 octane)?

 

Just plan on doing it every 50k or so.

 

Use premium fuel and drive it like you stole it.

 

That problem appears to be isolated to the turbocharged engine Mini was using prior to the introduction of the Countryman, and does not appear to be an issue with the current N18 engine design.