Power Steering Lower seal replacement?

I have a bit of a leaky lower seal on my power steering box and was wanting to change it out but how to remove the old one? I was told by one fellow that did his that he removed the Pitman arm and the snap ring then started the car up and turned the steering wheel and the pressure inside the box blew the seal and retainer out. Has anyone done this job and know if this works or have any other tips?

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