You can watch the slave as you press in the clutch if it doesnt move back an forth then you need to bleed it out ,, when you bleed it out it takes a moment ( clutch in out many times ) before it gets back hard...I use a power flushing system by Snap On tools an It works great ...To be honest if it was me Ill replace the slave/master at the same time they both do tend to go out ..Just like light bulbs they have the same amount of hours an time on them they will tend to go out soon after the other one does