It's not the slave cylinder, it's the clutch fork hinge.
The sound went away for a while because you jiggled and moved it outside its normal throw. Moved a little bit of shit around on the pivot so it quit squeaking for a bit.
The grease you sprayed into the slave cyl won't hurt anything but didn't do anything either.
http://www.ft86club.com/forums/showthread.php?t=117266
http://www.ft86club.com/forums/showthread.php?t=115631
http://www.ft86club.com/forums/showthread.php?t=56882