Get a buddy to help you with this. Engine off. Pull the rubber inspection plug in the bell housing near the line. Watch the end of the slave cylinder while you have your buddy push and hold the clutch pedal. If the end moves forward and then sinks back it's a master cylinder bleeding internally. If that's OK, determine if you're leaking fluid. If you bleed and top off the system, then after a day or so of driving (whenever it acts up) your fluid level is low, it's a leak. If you don't see fluid coming from the hose connection or master cylinder, it's a blown slave.
If you can't see the end of the slave cylinder, use a screwdriver to feel for it.
Also, I'll mention this just because some people honestly don't know: when you're bleeding the system, shut the bleed screw again before the stream completely dies off. If you leave it open longer than that you're very likely to get air back into the system. I once spent literally hours trying to bleed brakes (when I was new, I swear!) and never got the air out for that very reason.
Make sure you put the right fluid in there. I've seen lots of people put PS fluid in there and screw everything up. If that ever happened to your system, replace everything, it'll never recover.