Interesting....I do remember it being kindof a trick to get the balls/cage on the new retainer/shaft. (rubick's cube stuff.)
As for replacing the whole shaft, I chose to do so because it new the boot had been compromised for a much as 2yrs...maybe quite a bit more. With THAT much exposure to debris, I didn't want to chance re-using the same [outer] CV components. (with a new boot).
Plus, for less than $100/shaft, I couldn't think of what the downside might be.