The correct level is to the bottom of the fill plug, which is the 10mm hex socket above the drain plug. With the car level, fill it until it just dribbles out of the hole. It is possible to do this on the later cars from underneath if you use a long filler pipe, or from the top but you will have to remove the stone guard. It's less than a quart when filled this way, its less than 600cc if memory serves
