I had this exact problem with my rear shaft. It was about 20,000 miles ago so this advice should work if executed properly. I found a ton of water in the "Sealed" joint which corroded the c-clip and allowed it to do what you are describing.
Mark the position of the shaft to to flange. Apparently this is important, I didnt do it, but thats the word on the streets. It wont affect balance at all if you dont.
To get the shaft out of the pinion flange, you will need to get a centerpunch behind the flange with the bolts removed. You will see small access holes at opposite side of the the yoke. Use the centerpunch to kock the shaft out of the flange. Repeat the process for the T-Case side of things.
With the driveline removed from the vehicle, you will notice a cap on the back side of the Rzeppa joint. It is mechanically crimped on. With a small screwdriver, pry each tab up and remove the cap. Its full of grease, and in my case water, so have plenty of rags on hand. Wipe the grease off best you can, and remove the snap ring securing the shaft to the joint. The joint will now be held on the shaft only with the rubber boot. The collar that holds the boot to the joint will slide off, with some persuasion.
Thake the shaft to an auto parts store and find the correct snap ring.
To re assemble, pack the joint, boot, and end cap with grease then re-install the snap ring. Secure the end cap by using a chisel and work your way around the lip of the joint, hammering each tab into place.
Re-install and youre good to go.