Your corrected priority and filter pressures indicate that the pump and priority valve are supplying the system correctly. The problem is that both brake-release circuits are only receiving about 85 psi. Since both sides are equally low, I would first suspect the common brake-control/parking-brake valve, a stuck modulation spool, or internal valve leakage—not two brake-piston failures at exactly the same time. Verify full pressure into the brake valve and measure its outlet. Then isolate each brake line individually. Only if a brake circuit will not build or hold approximately 424 psi when supplied separately would I pull that steering-clutch/brake assembly for piston seals. That isolation test should prevent a very expensive unnecessary teardown.