By my understanding the serial number points to a series 1, 580L from late 90s.
When purchasing manuals make sure your serial number is within range for the manual.
Just to confirm, the oil level is full after the change, correct? (about 15 gallons needed)
Also, the hydraulic filter restriction alarm/light is not active, correct?
I found a 580L operator’s manual and see there is reference to a “pump charge procedure” after fluid change. I assume you/your-friend have seen that in the machine’s manual. If not, it states to see the Service Manual or Case dealer for proper startup procedure.
Unfortunately, I don’t have a 580L service manual to confirm, but I seem to recall applying around 5 psi of air pressure to the reservoir while another person starts and runs the engine at low idle. (This is from memory so I would recommend to calling your dealer to obtain the proper procedure)
In the original post referencing pressurizing the tank, what specific procedure was done? Did it involve anything that included running the engine at high rpm that might have damaged the pump by oil starvation?