My suggestions was the same at first.....
But have analyzed some SSP manuals about this regulator and a brake pressure valve on the rear axle between right and left wheels, it\s a quite smart sytem, that mechanically ajusts brake bias between front and rear axle, dependig on how hard a brake pedal is pressed at the moment, and between rear right and left wheels during cornering.
Got stucked this thing at the top position one one of our cars, front brake pads wear was increased and brakes were often overheated, while rear brake discs was rusted, the brake testing machine was shoving enormously high front braking and no brakes at the rear, fixed this regulator and everything became just fine.