NAPA p/n 7-180 I paid $6.59 plus tax.
It comes with instructions.
Remove the rag joint pinch bolt (7/16" 12 point) and with a prybar, slide the rag joint and steering shaft upwards to clear the input shaft on the steering box.
Make a reference mark on the steering box and the part the large locknut is on (the adjuster).
You don't want to reassemble it any tighter than that existing adjustment, unless it's really worn inside.
Using a drift punch and hammer, loosen the locknut, and unthread it from the steering box.
Now, VERY IMPORTANT, as you unthread the input shaft adjuster/seal assmbly from the steering box, make sure you keep pressure on the inner shaft, do not allow it to back out of the steering box, or you will end up doing a PITA complete disassembly and reassembly of the box.
I just did this job on my truck, and it was much easier than I had anticipated.
Just go slow and be careful.
There was a slight difference between the instructions and my box as for the parts to install to replace the seal, but it will be obvious to you what to do when you get it apart.