Well, I finally got to the bottom of why I was having trouble selecting low range. Well, in truth, it was not me, it was my wife whilst I was under the Disco. When the selector is placed in Neutral, sometimes it does not quite position itself precisely in position so that the little N light is on. If it is positioned correctly, it drops into low range every time. Therefore, note to self. Next time there is a problem with the Disco, let the wife look at it.....