See post "rear end shaking apart"
Forget # of reply but link is key:
https://www.napaonline.com/en/search?text=drive+shaft+rubber+center&referer=semantic&se=1#
Think the part was about $10. Beats $90 for assy. Guess I'm lucky with mine as still original with 255k on truck? When/if I need I'll try this route 1st. I've had my whole shaft in/out at least 5 times over the years just to make it easier for other things I was doing. I read on TDR the key for removing and replacing is to mark reference points on assy and mounting areas for exact location so reinstall gets it back in same place. Otherwise you could end up with vibrations. Also read that there are a few different assemblies with slight differences than whichever one originally came on the truck, that will fit, but won't be "quite right" and could cause vibration and won't last too long. Hope this helps.