Seat post repair

not your typical post here

calling all engineers and pneumatic experts or anyone who understand how a gas lift chair works.

right here we go, i have one of these:


its now not working properly due to losing air pressure, its not done too badly, i have had it since august and rode on average 3 times per week.
i need to figure out how to re-pressurise it-this is how it looks without the kind shock sleeve:



as you can see its a basic pneumatic compressed system, im not quite sure how the valve inside works and how it switches pressure from one side to the other-this is not really important, but basically the lever presses the sealing pin down a few mm and the seat goes down easier.

this is what the top of the sealing pin looks like:


i saw this and thought easy, i will simply link the the fox pressure pump up and pump it up and the pressure should slam the sealing pin back into place when i remove the valve, unfortunately although it does this it also loses about 75% of the pressure in the process of doing so.
this is the simple system i used to add air, surprisingly i got 250 psi into t but when i pulled the valve out it went back down to about 30 psi


any ideas or anyone know how they pressurise them in the manufacturing process?

i need a valve with a magnet on the end to pull the pin when the valve is pulled out or something, unless i can pressurise it from the other side

i probably should admit defeat but im reluctant becuase i believe it can be fixed some how