Sorry, but in my opinion, the main problem here is basically the typically 'cheap equipment' issue. Looks to be the same pump as in the Magom Bruder excavators, which many owners have had issues with, at least the early versions.
Cheap pump => low low efficiency => crazy high rpm constantly => hot hot hot (if the pressure is abnormally high, caused by some obstructions in the system that should not be there, or system pressure set too high, one can add another; 'hot', or two..
)
- Try reduce the system pressure to a point you got enough forces in the cylinders, but not more than that..Adjust the 'pressure relieve valve', if it exists in the system/pump..If it's even not there...well, there you go..)
- I would possible also try to do some mix operations on the radio; let the pump rpm down to e.g. 10-30% of max speed when no valves are operating (as soon as one of the valve servoes are moving, pump motor speed goes to max)
- Installing a compact PC cooler and fan in the system, on the return line before the tank, can help reduce the heat. A larger tank will also be helpful (not as much as a cooler). Even a fan blowing air out of the machine house will help a bit.
- Magom offers a heatsink incl. fan for your motor. Can help a bit.
- The early Magom systems was made to operate with brake fluid, not oil. Don't know what you're using.
- Evaluate replacing the old pump with the latest Magom version with a brushless motor (not the 900 ml pump..way too big here..) With or without tank as you wish..