Remove the REAR line on the master cylinder. Undo the large 17mm nut in the M/C & remove. With a small ‘Eazy-out’ remove the flared pipe seat, behind this will be the little plastic ‘Residual Pressure Valve’ & spring.
Discard the plastic valve & spring.
Refit the flared pipe seat back into the M/C.
Screw the large nut back in, then screw the line back in.
Then bleed the M/C at the union, followed by the rear calipers.
Bolt the road wheels back on & lower the car back down & take for a test drive!
(Removing the Residual Pressure Valve eliminates the rear calipers locking on when they heat up).
Some further info I found: