fuel additives
 

This may be more of a general question, but since I own a A8, I'll ask it here. Usually I fill my tank with non-ethanol 89 octane and only use the ethanol blend when I'm in a pinch.
With this fact, should I also be using any sort of fuel additives to keep the injectors clean or will the occassional ethanol blend fill ups do the trick just as well.