Is this what you are calling a check valve? I pulled up the online parts catalog, and they call it a relief valve. Also there is ZERO fluid leaking anywhere, if that makes a difference.
The issues I'm having is the motor will go down by itself when running in the water and also it will not trim up when I'm running it in the water. When I slow down (no load) it will trim up and down normal. So I trimmed the motor up and manually pushed down on the motor and it slowly goes down...