drivers rear -is- the furthest from the brake m/c
the lines run along the passenger side
Having one piston that wont retract should not cause you to “not be able to stop”.
Check ALL calipers for leaks. Look for any wetness around the calipers, lines, bleeder screws. Check behind the master cyl, on the face of the Brake Booster for wetness / leakage.
What is your fluid level in the master cyl reservoir?