Chris,
Your pump is lubricated by the diesel that leaks past the plungers. The bolt inside your red circle should be a hollow bolt and it should have a short pipe attached to it, so that the excess fuel can drip under the tractor when it gets too full.
If the inside of the pump has been cleaned or has been out of use for a long time, you can squirt a little very clean oil in through the plate that you have open in the picture.
It does not need to be regularly lubricated with oil, diesel will do the job while its running.
i have the pipe i just havent got round to painting it yet lol.
It was just that my manual said that it should be filled with oil through the leak off pipe.