#19 is the boot. Run it up on a slope with the side you want to work on up hill. Remove the pin and unscrew the clevis from the #16 rod, noting very closely just where it was before you moved it. A prybar or chisel should pop the boot out of the hole, slide it down the shaft, and replace, tapping the new one in gently. A little oil on the rod helps. If you had enough of a slope, you won't loose any rear end oil. I did mine in about 20 min., but had to fiddle with the brake adjustments for a bit longer to get them right. You don't have to be very far off with that clevis to have a big impact on brake function. Nothing other than that boot to keep the oil in.
I'd avoid twisting on that rod (#16) any more than you have to if the clevis is stuck. Use a small pipe wrench or vise grips to hold it when wrenching on the end. If you happened to twist it off inside, you have to take about the entire rear end apart to access. I have a rear axle seal on my 4000 that leaks that I've been putting off fixing because of that...