Welcome to 2CarPros.
If there are no leaks or fluid loss, it has to be the master cylinder has failed again. Take a look through this link:
If you read through that and determine it is the MC, here is a link to help with replacement:
I attached an exploded view of the MC for you to see. Honestly, if there are no leaks and the fluid remains full, this is my first suspect.
Let me know if you have questions or need help.
Sunday, April 28th, 2019 AT 6:09 PM