If the pedal slowly goes to the floor when holding pressure on it, chances are the internal plungers are bad and allowing fluid to bypass. Take a look through this link.
If you determine it is the master cylinder, and it does sound like it, here is a link that shows in general how it's done:
The attached pics are specific to this vehicle (not sure if you have a right or left-hand drive).
Let me know if there is something I can do to help. Also, there were no 4 cylinder engines offered in this vehicle, so let me know which engine you have.
See pic below.
Images (Click to enlarge)
Tuesday, August 24th, 2021 AT 8:54 PM