Going to buy a car.. The tranny runs very smooth, doesn't seem to slip at all, doesn't hesitate.. But the guy told me he never had a flush on it.. Ever.. He told me, that if a car has never had a tranny flush, to never get one, bc once you do, it cleans the lubricant from the gears, and that's when your tranny fails.. Is this true? I was thinking if i just replaced it, it would be fine but i dunno?