I have rebuilt power steering pumps a few times over the years cause I keep my cars so long.
They are dead easy. The rebuild kits, that are purchased thru the dealer, consist mainly of O-rings and seals to prevent both internal and external leakage.
There is a magnet inside that needs to be cleaned but other than that no other hard parts need to be changed.......or can be for that matter. If it'* that bad, visit the scrap yard for a donor.
If you open it up, you will see what I mean. There really is not much to it.
I rebuilt my first one when I was 20 many many years ago.