On the play, loosen that large nut with a hammer and punch, then try to gently tap to turn the center piece in. There are 2 holes for a spanner in the face of it. If you can find a spanner that fits, it's better than the hammer/ punch method.
On the leak, I don't think you can get it to stop. My shaft was rusty like that, and it didn't leak for a month after I resealed it. Then it was back to dripping. I ended up replacing the whole center assembly with the one from my donor truck, and I didn't reseal that one, just put it in.
The good thing was, the truck used to feel real quick when you turned the wheel, like it had too much power steering. When I put the new piece in, I tightened it up and it was slightly stiff, so I backed it out about 1/8 of a turn, and it feels just perfect. I was reading in the FSM after I had done it, and I by luck did it just about how I was supposed to.
