This just started tonight: I'm stopped and after a minute I notice the car is drifting forward. I brake harder, it stops, but the pedal sinks and it starts again. I checked my brake fluid and it looked pretty low so I bought some DOT 3 and added to the max line. That didn't do anything, apparently. I can come to a full stop just fine, I just can't stay full stop unless I use the parking brake to assist.