Office Chair Repair: Fixing Gas Lift Swivel Chair Lowering Issue for 75kg User

I warmly welcome.
I have such a problem, I was looking for help on Google but I found nothing helpful.
I have a swivel chair with a lift (probably a gas one, but I don't know if it is a gas one).
And the problem is that when I lift the chair all the way up and sit down, it slowly lowers on its own, what should I do?
Could it be before Santa's expense (gift)

Of course, I will add that my weight is somewhere around 75 kg, so the weight of the body sitting on the chair is not an option.

Replacement o-rings are leaking.

And where is this O-ring located in the armchair? at the bottom or at the top of the telescope?

Usually it is a non-dismountable element.
The o-rings are usually located where both pipes meet, and there is also a height adjustment valve gasket, which is probably the problem.
When disassembling the actuator, remember about the tensioned spring that expands the actuator.

Added after 20 [minutes]:

Some chair springs are filled with nitrogen, the easiest repair is to replace them with a new one.
I recommend information from the website: www.dynamicseat.pl

Repairing something like that and undressing itself can end badly or very badly.

arekb81 wrote:

Repairing something like that and undressing itself can end badly or very badly.

And I let the gas out of the actuator at my own request or stupidity. Which is good on its own. It can be somehow supplemented with compressed air is there something that resembles a valve from the bottom? I was looking to buy an actuator on the net but I can not find one in Poland
kgl din 4550 klasse 3