I've replaced a couple slaves, so I did some searching before I bought parts, and the one thing I saw repeatedly was slaves bought from parts stores are junk.
I got mine through dial-a-clutch.com, and both times the slave was identical to the stock slave I was replacing.
I also did the whole clutch both times, got the whole package through dial-a-clutch, and got the Luk kit, which came with the slave. I can't remember if the slave was a Luk branded part or not, though.