Ok, the slow drop indicates you have some leakage at the one way check valve feeding the accumulators. 15psi/minute isn't terrible.
Let's check basic health of brake system.
1) monitoring brake pressure, pump brakes till pressure is around 1400.
2) start machine and observe pressure climb. At what pressure does it stop? Should be roughly 2200 psi. This is cut out psi.
3) pump brake pedal watching pressure, do it slowly and deliberately, your watching for the threshold of when the pressure stops dropping and begins to build back up. This is cut in psi. This should be close to 1800.
4) repeat the process 2 or 3X to get an average.
5) now we gonna check max brake charging, once the brake pressure has reached its cut out pressure, we need you to curl the bucket back over relief. You should see an increase of at least 200psi. You should now be at or near 2400 psi.
I suspect this is where your problem lies. Based on info you've already provided. If there isn't enough separation between max charging and cut out pressure, active brake charging runs over the pressure reducing valve for max charging. Since the sensor can't see the value it wants in 60 seconds, it continues to throw oil at accumulators instead of fan. What you'll need to do is adjust the reducing valve PB at the central valve. On that same block that you swapped MA5502, on the bottom edge, facing the trans is the pressure reducing valve for brake pressure. You want to loosen the jam nut and adjust it in until you reach 2400 to 2450 while holding bucket over relief. Good luck . BTW, make sure to place the frame lock before climbing into the turning joint. You could probably do this from underneath if she doesn't have belly guards.