Seeking opinions on TO-30 hydraulic problem

I opened up the right inspection port and found the following. I was parked on a 10-15 deg downhill slope and the fluid level was and inch below the top rim of the pump (low even for the incline). The fluid was a brackish brown with some solids. With the tractor turned on and the PTO engaged I did not observe and fluid spraying from the cylinder area.
The middle area of the pump where the PTO shaft goes through was generating splashing which I assume was normal given the low fluid. I did not see any turbulance on the outside of the pump area indicating a crack.

I checked operation of the quadrant linkage. Moving the quadrant down causes the linkage to move about 1/2"inch towards the back of the tractor below the area where the return spring is attached. I could manually push that area back a little more but it was pretty stiff. With my hand in the "soup" I was unable to detect movement of the control valve when I operated the quadrant. I was unable to manually pull the control valve to lower the lift.

I am assuming the control valve is stuck which is why the lift won't come back down. I'm not sure how much movement there should be. I am hesitant to just pry at it for fear of bending stuff. Is my best bet to pull the PTO, drop the pump to "renew" it. Could there be another problem?

I think the sluggishness and shaking of the lift may be partially due to low fluid levels and partially due to "sludge" in the valve assemblies.
If I drop the pump should I buy a complete rebuild kit or just assume the lift will perform correctly if it is disassembled cleaned and reassembled? How do I guage the condition of my existing vavle assembly components?

Does anybody have a source/part number for the large pump pan gasket I would need if I dropped the pump. I am only able to find "rebuild kits". Can I just use a generic gasket compound?

This is the first time I have ever worked on the hydraulics so I appreciate your opinions. Thanks for your time.