Humm...l'm not so sure Brock
Look again at pic #9 and read the big clue in the comments immediated below the pic.
Then go to pic #12 and read the comments there.
The seating land for the coupling should be clean and not fouled with it's own ground up aluminium from a chattering hardened steel coupling.
The hardened cush rubbers and worn aluminium guides should have been replaced. And then the 4 final drive attach bolts loosened and the final drive realigned to fit the new components. Otherwise, tis a waste of time with a new 'O' ring.
Just a thought.
Cheers the can:-)
