..so he explained it well :
https://www.youtube.com/watch?v=oeSa9cV6CMQ
Good job...
However, he should used recommended parts from the manufacturer. If something were to happen after he replaced the o-ring(s), the manufacturer will no longer be liable for the failure.
One thing I know is that Hmong and a lot of people used the jack as the only source to hold the vehicle up. Jacks (floor and the ones that comes with your vehicle) are design to lift up the vehicle to do quick tire change or whatever but not if you want to work under the vehicle. They are not design to hold a vehicle up while doing work underneath or for long period of time. Use jack stands to work under the vehicle.
I never work under my cars with just the jack itself, I use a jack stand to put the pressure off of the jack. I will keep the jack there just incase the jack stand fail. It's safest to have double the protection...
I had a cousin that passed away due to his jack failing (he did not use a jack stand) and he was crush under the car... he left a wife and 3 little kids.