Brake pedal gettin hard indicates insufficient power assist and it could be due to a faulty power booster or inefficient vacuum from engine. Check the vacuum hose for signs of collapsing and leakages.
Transmission fluid would cause the master cylinder seals to soften and expand resulting in internal leakages resulting in the pedal sinking when held.
If transmission fluid ahd gotten into the system, you would have to clear the system of the fluid failing which replacing the master cylinder would only be temporary before any fluids in system backflows and gets to the master cylinder and damages the seals again. It is a matter of time.
Any cause of brake pedal sinking is leakages in system. Check for leakages, especially from hoses or joints.
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Monday, February 22nd, 2021 AT 11:22 AM