I have 2 things I wanted to mention after watching this:: I did not see an o-ring go in there, I have heard it helps to stop oozing oil out a wrong place, and secondly, I didn't see any oil or lube on the drum bearing....
Never have put the o-ring in there, and never had any issues not using one. The clutch drum bearing is not that difficult to get to with an inboard clutch, if it would have been an outboard clutch it would have had something put on it.