Dave, the problem is he replaced the slave and has total air in the system. Your good experiences with mighty vac are now invalid, believe me, and you don't need to ask me why I know this.
A power bleeder may not work so great in this situation either.
The slave has an air pocket condition because of design and the nipple not being at the absolute high point of the slave. Once air gets in it is plain tough to get out which is why if you tilt things like pulling the slave out or raising the rear of the car very high you can usually solve the problem.