Welcome to Nissan power steering. They ALL leak. Every Nissan I've owned (and that's been about 10 now) has leaked power steering. Even my G35 did at 40k miles. stupid.

anyway, yeah I've rebuilt a pump on my Maxima before- it's not too involved. the procedure is shown in the FSM.

The steering rack rebuild is a bit more difficult, but if it's just that one seal it shouldn't be too bad.

BTW, I just said screw it and converted mine to a manual rack. way more room in the engine bay, more power, and less leaks.