I think the MMIs are more tailored towards using your common sense than how well you can regurgitate what you read in a bioethics paper. Certainly it'll help, but I don't think you'll be disadvantaged if you use your own morals and your own words (without needing to throw in words like "patient autonomy", "beneficence" or "justice" around) to justify your answer.
My only advice is to be yourself, don't make it sound like you're trying too hard. I think the adjudicators will be able to tell if you're trying to recite an answer or trying to answer based on what you think they want to hear vs. what you actually believe. It doesn't matter what you say, really. What matters is how well you can defend it - do you look at both sides of the issue? Do you rationalize your answer appropriately? Does it sound like you have a good sense of morals and ethics? Are you an empathetic person?
Furthermore, it sounds like your grades are up to par, but perhaps some humility might be necessary? I think it's somewhat apparent (dare I say - obvious?) that you have to meet the cut-offs in every section. A 98 composite, while admirable and perhaps something to brag about, means nothing if you miss one or several cut-offs.