You will need a really good pitman arm puller. I mean, really good. The cheapo Harbor Freight ones are known to break. You could try soaking the splines beforehand to help. I would douse the area daily, for a week.

What exactly leaks?
Is it leaking where the steering shaft enters the box?
If that is the case, that seal can be replaced by itself. I had to do mine a few years ago. Disconnect the shaft and pull it away from the box, remove the big disk cover, and replace the seal on that disk. All while the box was still attached to the frame.

85 4Runner - With NEW Marlin 4.7 Gears!! It's a whole new beast!