Melrose 4r

My truck has 186k on the original power steering box. I've adjusted the slop out of it as best I can but I can still see there is quite a bit of freeplay on the input side before it starts to have any effect on the output side. All the ball joints, tie rod ends and Idler arm are new. So I am considering going in there or getting a rebuilt box.

Question: What specifically on the input side would cause the freeplay? The box is not leaking so this would be the only reason I have to go in there and I'm trying to build a case in favor of it.

Thanks,
Thomas