They have an obligation to fix this correctly. However, I’d contact your state’s Consumer Afairs division of the Attorney General’'s office and research you state’s lemon laws…just in case.
“I think you have very strong grounds to demand a replacement vehicle.”
Not yet. The lemon law is the way to do it, and that will take more time.
Here are some points which you may need answers for -
For how many days exactly was your prius with them? This is the first question that comes up while availing lemon law.
copy of the repair order stating your exact complaint. What was the solution they tried.
Do you have all the receipts from the time your prius was first sent to dealer.
these are the basics.
Since lemon law differs from state to state, you need to check laws specific to your state. you can check this site http://www.lemonlawamerica.com/
but i wish you get your prius back properly in condition, but i can understand that you cannot forget what you had to go through all the days in between. Are you by the way environmental conscious? I asked because you went for prius. I too am 
I believe in the sustainabilty concept and read things about it in the internet when ever i am free. anyways good luck with your prius.