It only happens when the car is jacked up on the front, driver's side.

I changed my brakes yesterday and noticed brake fluid was coming out of the bottom of the brake booster, where it meets the master cylinder. After I got the brakes changed I pumped the brakes, and no fluid leaked out during the pumping of brakes (had a friend with me). It doesn't leak right now, and like I said it only leaks when it's at such an angle like that.

what could be the cause?

 

Coolant was coming out of the brake booster?!

 

umm, i'd read the title of the post before making remarks like that. Thanks though. I'm sure that everyone could clearly notice "brake fluid leak" in the title, and nothing but talk of brakes and brake fluid, and one mistaken instance of "coolant" instead, would make EVERYONE think that there's coolant in the booster

 

Possible seals in the master CYL itself. Fix it before it eats your paint TOO much... You do know that brake fluid eats paint, right??

The master is basically just a plunger. When you press it in there are wiper seals that are supposed to keep the inside walls of the CYL itself clean. They could be dry or ripped. So when you let off the brakes it 'drags' fluid back twords the rear of the master CYL.. Thus accumulating and dripping down where the booster meets the MAS CYL.