As a part of my 6spd swap, I put in an ACT 6-puck with the heavy duty PP. The slave cyl. was completely empty of fluid when I put it in, so I bled the slave cyl. following Subaru's recommended method (opening the bleeder while the clutch is depressed, then closing the bleeder valve and releasing the clutch).

Now, the pedal is very soft until I reach the disengagement point and it's stiff during disengagement. The pedal will return on its own, but it's not a smooth operation.

I'm wondering if anyone knows whether there may still be some air in the lines, or if the slave is bad?

When I had an ACT street disk when I had the 5spd, the clutch movement was very smooth and stiff through out.

 

there might be but i would say keep pumping the clutch that what we had to do with mine and it finally worked

 

Dealt with this on a couple of STis/WRXs, seems to be more of a bitch with them than other cars (in my experience). Bleed the lines thoroughly, it's best done as a 2-man job. Likely not a bad slave cyl unless you pumped the clutch too hard while the slave was clamped and blew the seal.