Hydraulic cylinder does not fully retract?

Hello,

I have a problem with my Kuhn GA 7301 rake. The left cylinder (as seen from the cab) no longer retracts completely and stays 2 cm too far out. Now I have the problem that the safety catch no longer engages, and when I unclamp the rake, the pressure in the hydraulic hoses drops, and the rotor falls down.
I suspect that there is air in the cylinder and that is why it is not fully retracting.

I thank everyone for an answer as to what you think the problem could be.

Greetings