Hi guys can any one tell me is it a difficult job to replace the o ring on the throttle shaft on a td 42 fuel pump whilst it is still in the car,the engine runs great its just developed a fuel leak around the throttle on the fuel pump,the engine hasn't ran for a couple of months due to a conversion from a rd28t to the td42,prior to this it was fine so i am guessing the o ring has gone hard,there is a slight bit of movement in the shaft,any help would be greatly appreciated,i don't really want to remove the pump and have it over hauled unless it is totally necessary.