I'm still saying get a lawyer.
One of the reasons is this: if you do have to redo the rotation(which I believe you should not have to) then a lawyer will know how to draw up a contract with the necessary provisions. That is, if the agreement states that should you do well in your redo, your old grade disappears, then it becomes legally binding.
Keep in mind that without a good contract protecting you, your grade is at the whim of the administration. Even if you do extremely well next time, if they want to keep your old grade on your record, they can, unless a legal contract that they agreed to states otherwise.
Also, if you have to go that route, do the rotation WELL AWAY of where you were previously. Also, the new site should have NO knowledge of your remediation, so that you can be evaluated fairly.
Another reason I think you should get a lawyer is the fact that, from your perspective, it sounds like you've done nothing wrong. It merely sounds as if you didn't get along with your evaluators. That's no reason to fail a rotation. If there is a start-time to rounds IN WRITING and you always showed up at this time, then there is nothing that can be said against you. NEVER imply that you were late! Just state that you always showed up on time for rounds as per the posted/printed/emailed schedule - say nothing more.
That's my opinion. I believe in justice, and the OPs situation does not sound just in any way. What do you have to lose?
Let's play a little game theory:
1. You do nothing: you get a fail grade, have to repeat the rotation likely at the same site. You could fail again and therefore have to repeat the year, or you don't fail but still have that stain on your transcript and therefore will be unable to apply for any residencies the least bit desired. In other words, you lose.
2. You arrange to meet with the dean, give him the story, and try to challenge the grade. The administration is more powerful than you and will stonewall you completely. You will still have the fail, you will still need to repeat, you will likely fail that because they are vindictive, and you will have to repeat the year. Also, the vindictive administration will make your life difficult for the future, and your MSPR will likely have a few negative words in it as retribution for your challenge. In other words, you lose even more.
3. Get a lawyer, meet with him, get the facts straight and the evidence lined up, meet with the dean, and try to challenge the grade; failing that you draw up a contract stating what will happen on your remediation. Going the legal route protects you and makes the administration likely to settle because going to trial is expensive and time consuming, even for a large administration. They'd rather it not come to that. Plus, if there is no legal, provable reason for your failure, they will have no choice but to reverse it. Your chances of winning are best here.