OK so I once again disassembled the Valve and took a look, I cant tell what may be the problem.

I missed one o-ring, the smallest one in the inner pat of the piston. It is quite flat, but do you think this would cause the described symptoms?

After re-assembling and starting the car, The car goes up with manipulating the arm up, but wont come back down. I'm not sure if its at its maximum height, but its definitely not too low. It looks about as it should be. But Nothing seems like it will change with the weight in the back as Valve doesn't seem to be doing its job...

Any Ideas?