Hey folks. I hate asking 'dumb' questions and betraying my ignorance in front of y'all, but I'm sure one of you guys has to know the answer to this. While driving my wife's e46 (2005 330xi) I noticed the brakes felt a little...shaky. I mentioned this to my wife and she said it's been like that for a while. I popped the hood and checked the brake reservoir and it appears to be empty. A friend told me this happened to him and you can just add more brake fluid, but I've always heard you can't let the fluid drop below a certain level or adding more will cause air bubbles. SO... can I just top it off and keep an eye on it (suspecting a leak), or does the system need to be bled (or even flushed)? Is it safe for her to drive it to work tomorrow? Thanks in advance for any advice.