3 point hitch stays up

Hello,
I have a 7000 maroon belly with an issue of the 3 point arms raising all the way when the tractor is running even though all levers are in the position to have them lower. When I turn off the tractor the arms go all the way down and then quickly raise when I start it back up.
When I push down (on what I believe is the pluger for the traction booster) it moves freely, but gives a sort of spitting sound and you can def feel it in the small line underneath it. Nothing changes with the arms when I push down on the plunger. I've attached a pic showing the plunger and the line. Thanks for your help!

Traction booster plunger must be UP/OUT as far as possible. There is probably rusted/stuck linkage holding it down, which raises the hitch.