Hi mate, It sounds like youre throttle shaft seal has gone. In the top of the pump is a bush that the the shaft rotates in, also an O -Ring seal. Not an uncommon fault nor difficult to fix. My Friend replaces these for a living and always takes the top off the pump. The repair kit is usually, shaft ,seal and bush. Any good diesel specialist can do this repair in situ in about an hour. :tappity: