The last yank that needs to be pulled is roughly at the 11:00 mark as you face the vault. Try - going around the room pulling each yank in a clockwise order - don't pull the last yank, instead go back around the room counter clockwise and pull down all the yanks that went back up. Check them again and correct any that have gone back up - when they are all down THEN pull the yank at the 11:00 mark.
This was the fastest method I found for doing this puzzle.
Wyv
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