At my dealership machine was not there and they told me same story of master cylinder going bad. I improvised, used a syringe and sucked the old fluid out of the container at the top of master cylinder. took it to the lowest level and then topped it up with new fluid. started bleeding the fluid from the bleeder valves and again when it reached the lowest level, I topped it up. I never let it decrease below the minimum so that Air may not enter the system.
Drove for few days and then repeated the exercise again. After repeating the process for 3 to 4 times, I called it a day and the performance of brakes was improved significantly.