my transmisson was just rebuilt is there a certain time frame when a trans flush is a good idea? or should it never be flushed? being that its brand new, what mileage would you consider it not to be a good idea? my old trans lasted 165k miles until my internal seperator broke and mixed trans fluid and radiator fluid. the trans was replaced in 2018 but over the last few years had several issues with it and ford finally ended up rebuilding it a couple months ago. now with a new motor going in, im hoping to have this last many more miles, so i need expert input from the peanut gallery.