#1 only. Unless the booster is bad too - unlikely.
Mushy brakes can be caused by a number of things. Master cylinder failure doesn't cause mushy brakes. A bad master cylinder will cause the pedal to slowly creep towards the floor when you have solid pressure applied to it.
ie: you step on the brake pedal until it is solid and firm. As you continue to apply constant pressure, the pedal is slowly sinking to the floor.
I checked the fluid and its a little low. I hope its not leaking somewhere! I have SS lines from Dali, with carbotech pads if I remember correctly... with the ATE Super Blue Brake fluid... why would there be less fluid in the reservoir?
If the fluid is low, it is leaking somewhere.
