It's been a couple years since I was into my 5spd ZF on Thumper... I can't recall exactly what the couplings looked like at the slave but it could be as simple as a bad o-ring seal (if there is one... like i said it's been a few years) where the hydro line connects to the slave. It could be a junk slave too. I haven't had any problems with the aftermarket parts i get from O'Reilly's... I've only got 2 or 3 slaves from them but haven't had a problem with them. You could have crossed your threads, had dirt in the hydro connection... there are a 100 different little things that could have happened to make it leak. I'd take it apart clean everything and make sure you have good solid connections. Then have someone hit the clutch a couple times to see where it's leaking from (whiles it's apart of course).