Advice: Buy 2007 Toyota Sienna where transmission fluid hasn't been changed?

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I'm looking at a 2007 Toyota Sienna and the owner says she doesn't think the transmission fluid has ever been changed. It's got 75,125 miles on it. What kind of transmission fluid comes in the 2007 model? How often should it be changed? Is this a serious cause for concern, if other maintenance has been kept up? As a note, the transmission fluid did smell just a bit burned, but was still only a slightly dirty pink color and had no debris whatsoever in it.