I know they are professionals but sliding the outer seal of the main ship bore shaft on the prop shaft can be nicked and scratch. any seals installed between the damage shaft 5:22 can fail and leak. While hammering the out seal in place for nut insertion the hammer can accidentally hit the prop shaft and damage
This video does not show the engineers replacing or putting in the new Seal Material. It just shows them pushing the Seal housing up to the shaft housing.