As I recall your machine model is a pretty old work horse.
Your explanation of the problem needs a bit more information. Where is all the hydraulic oil draining to? Is it going outside of the machine and onto the ground or into the final drive that the motor is driving? All hydraulic motors have an extra line that allows the slight amount of leakage in the motor to just drain back to the tank, i.e. case drain. The line is usually a lot smaller than the feed line to the motor. Any motor case drain flow will generally be less than a steady flow, more like droplets. A high flow of oil through the case drain hose will indicate that something is broken inside the motor. Motors that drive systems that have the potential of running away, such as a track drive motor going down hill, will have systems inside the motor to prevent that. The relief valves and all the rest of that stuff are nearly always designed to be inside the motor itself. Case drain filters are usually a low pressure low flow affair. One would generally cut them open and check for loose metal particles being caught that came from damaged motors and such. Almost all case drain filters are designed with a bypass mechanism installed in them so they don't blow up when something bad happens.
Fluid is going thru the final drive side. The original problem was the fluid was leaking from the float seal and drained all the fluid on the ground. I took final drive gear out and found the motor shaft seal was blown causing the float seal to pressurize and then blow.
So i removed the final, and motor off and apart put a new float seal, shaft bearing and shaft seal, put it back on thinking cause was a bad seal and worn bearing. After installing all back together except the gears in the final and the final cover on. Filled It with hyd fluid, got the air from lines. The boom, bucket, swing all worked. Then i went to move the drive motor and the fluid blew the new seal out.
So then thought it was case drain filter, i put a new case drain filter on and put another new shaft seal in added new hyd fluid in and tried It again, and it blew the seal again immediately.
That’s were I’m at now.
That’s about best i can explain.