You recently advised somebody who was thinking of buying a diesel car to take in to account replacing the DPF after three years. I have a one-year-old diesel Qashqai and, although I am aware after reading your column that long runs and high mileage are essential to preserve the DPF, I was not aware that they need replacing after three years. If this is the case I really think that this potential expensive replacement should be pointed out by dealers when selling diesel cars.