Well, I'm about to rebuild my slave cylinder, so I'm going to find out a few things. I have a little leak under the slave cylinder, so I suspect the "o" rings and or the oil seal on the inside of the cylinder are leaking as well as the gasket on the case. I have no problems with the clutch operation, just want to fix the leak. I have all the new components to rebuild it.
Don't know if you have "O" rings or oil seal leaking inside. If your case gasket is good, you may not know what is going on inside the cylinder.
The Banjo Bolt is the fitting on the line going to the Slave case.