I asked the guy about my pedal bleeding off slowly, and he reckons it has to be the master cylinder, not the slave.
The slave will only leak fluid, or suck in air. Good way to tell which is stuffed (master or slave) is to block off the line and press the pedal. If it bleeds off its the master
He rekons 1 in 50 or so come brand new that are stuffed, so be aware, you can get a dud newie....