My eldest son runs a Volvo V50 2.0D and has now covered 125,000 trouble free miles. He has never changed the cam belt and his specialist Volvo garage who has carried out all of the servicing assures him that it is not necessary to change the belt until he reaches 150,000 miles. Your column normally advises cambelt changes at about 75,000 so is he pushing his luck or getting bad advice?