I have used this method--its messy as hell,but usually works well..
Take the pitman arm off,remove the snap rings on the shaft holding the seal in (I think most boxes had 2 of them )--then put you biggest oil drain pan under the steering box,start the engine,turn the wheel to full lock and hold it there a few seconds--back off and repeat if the seals dont blow out into the pan right away..
Best to have a bag of speedi-dry handy!..it beats having to use a pick to try and pull the seals out...
Some prefer to pull the top cover off the steering box and pull out the pitman shaft and use a deep socket to drive the seals out from above..
Edit--if you can move the pitman shaft side to side,it is unlikely new seals will stop the leak,if that bushing is hogged out at all..that has to be replaced too..