Do a search, this exact problem was discussed a few weeks ago.

Found it for you!

I think you're doing everything right. The only thing I would suggest is to put a little rotational force (a pipe wrench or*) on the slave while heating and tapping. Good luck and be careful!
Vibration and heat will probably be the key to breaking loose the aluminum oxide. I hesitate to suggest an air chisel but if all else fails you might be able to disassemble the slave at the plunger end and drive it out with the air chisel. Again be careful the last thing you want to do is damage the bell housing.

*Large vise grips could give you some back and forth motion once you see a little movement.