I'll jump back in here and ask a couple stupid questions:

1) Do you have to pull transmission from the car to pull the tail-shaft?
2) If you did cut off that ear that holds the pin in, would the pin slide out so you could replace the O-ring?

If the answer to both the above is yes, then I could see the benefit to trimming the ear, and then adding a bracket to the bolt to hold the pin in.

Wouldn't this be an easy fix for us shade-tree mechanics would don't want to pull the whole tranny?