The tranny is going to go eventually no matter if it was a perfect example or not, and certainly won't go at a specific mileage. Mine went till 150k. I believe defective trannys are those that go within the first 50k miles.

Bottom line is if you're buying an automatic transmission car (from any manufacturer), you have to be prepared to put in a new transmission if it goes...just like in a manual you need to worry about the clutch and all of that, an automatic will wear out eventually.