Actually you may find that your Perkins
has a little rubber grommet insert that goes in to the aperture on the fuel pump
first, the fuel pipe is then pushed in through the centre of this grommet and the olive on the fuel pipe sits snugly against it, then the hex nut is tightened, don't over tighten the hex nut, just sufficient to stop the leak. You may have trouble getting the old rubber grommet out, it's fiddly. (I use a pair of stainless steel
Brilliant engine, virtually bomb proof if serviced correctly.