Hello everyone, has anyone ever had a bake master cylinder go bad on there is. I have been searching but haven't seem to many. I have a 07 Lexus is 250 with 130k miles. I a assuming it still has the original brake fluid, and I am experiencing a sinking brake pedal at lights especially on down hills. I am not losing any fluid so I am assuming it's the master cylinder. Any imput??

 

If there is some doubt at all replace it! Brake failure is the worst event ever.
Fluids should be flushed every 2 to 3 years to prevent damage to the system.

You do know the engine tune and health plays a roll in break pedal height and brake assist. A poor running engine has low vacuum. Low vacuum means less brake assistance/ more leg power to stop the car.

If however the engine runs well and you mash on the brakes, the pedal should be solid and not sink. If the pedal goes to the floor, replace the master cylinder and have the system pressure bled.