Having gone through UMich's application process and been accepted there, I can tell you that it's good to write whatever you feel will be easy to talk about in your interview. Don't repeat your PS, but if you must talk about the same experience just take another angle to it.
For example, I talked about my EMT experience in one paragraph of my PS. In my UMich secondary, I went into greater detail and mentioned some things that weren't touched upon in my PS. I talked more about why I did it in the first place, how it changed my outlook, what it means to me. It's great fodder for the interviewer--it helps them ask questions that turn into long conversations.