> I'm not sure if this is a safety issue or not as the pedal feels fine
> as long as the engine is running.  Do you think this can wait until a 
> more convenient time?

NO.  Find the cause NOW.  You have a plus on your side-- you can hear 
the leak.   Have a helper trace down the leak with your hearing, you 
should be able to find it.  The leak is possibly never going to 
change your braking... but if it does and you have catastrophic 
failure you, your loved one, or someone else's loved one could be 
dead.  All because it wasn't convenient.  Pay to have the leak traced 
if you must but do not f&ck around with brakes.  Sorry for the 
lecture.
-dan