YM2002D hydraulic cavitation - Air Leak? Control Valve part?

[scooter133]

YM2002D After about 15-30 Minutes of using the hydraulics (Bucket or 3Pt) the controls get sluggish and or cavitate.

Replaced the Hydraulic Oil
Replaced the Hydraulic Oil Filter
Cleaned the Oil Suction Screen
Replaced Hydraulic ram O-Ring and white washer thing
Replaces all the O-Rings when replacing the Control valve face.
Replaced the Hydraulic Pump
Removed the Bucket Control Joystick Valve box.
Pump output dumped into 3Pt Valve Control box
(Eliminating any of the Bucket Valve and hydraulic lines)

3Pt Mower attached, started cavitating when lifting at 30ish minutes into the mow.

cavitation with Bucket: acted jittery, Up and Back were jerky at best. then it was like we lost all hydraulic pressure.

cavitation with 3PT-Mower only: lifting became jittery, like it was lagging behind the controls. responded erratic.

I thought there Might have been a Leak on the Filter Screen cap. (The 3 Point Circle cap with the 10m screws)
Though upon further inspection the leak is coming from where the left Rear Axel Gear box bolts to the main engine body, just above the filter screen cap. Actually a few places at that joint.

The pictures show some shiny spots in the cracks between the two chassis pieces. they apparently leak much more than I thought. like a lot more.

Question: being so close to the intake, could after the tractor and the hydraulic fluid heating up, cause air to be sucked in to cause the cavitation?

Question: Could this be one of the spring, o-ring contraptions that control the pressure? The Numbered Items below.

Yellow parts re where I see the oil seeping from.

 

[winston1]

Your main relief valve is the one on the top right of your picture. It would be set about 2123-2275 psi with engine at 1500 rpm and warm fluid.

Your safety relief valve is the one one the bottom left. It's function is to relieve such as when your going down the road with a heavy implement and hit a pot hole. Your implement bounces and causes high pressure. It should be set at 2417 to 2702 psi. These numbers are out of a 220/226 manual. I am confident it is the same system you have . I owned a 2002D for several years.

You are sucking air into the suction somewhere.