My guess would be that if brass is ok for plumbing and musical instruments, you don't need to worry. Lead increases the machinability of brass, so the only question in my mind would be how much lead content? The lead content in brass locks and keys is much higher than brass used for the applications I mentioned previously.
My Copper is brass, but the 510 receptacle is steel. There is nowhere juice would contact the brass on my Copper unless I overfilled and got sticky fingers. The question then is, is brass safe to use in mods, and that is where I would want to know lead content.