Suddenly I have a clutch problem on my 78' 280Z.  Without starting my car first thing in the morning I can shift the car in all gears.  When I start the car I depress the clutch pedal to shift and I can not shift in any gear.  At this time the clutch pedal has little resistance.  If I pump the clutch pedal several times I am able to shift in all gears.  At this time I notice that the clutch pedal has more resistance.  Clutch fluid level is full.  Do I have a valve problem somewhere.  If it is a valve problem would it be better to buy a new or rebuilt one or put a kit in it.  Thanks! 

Sounds like you need a new slave cylinder to me.  Not a big deal and an inexpensive part.  The hardest part is bleeding the air out.

 Agree with Ala KaZaam ^. Usually if one pulls the rubber boot from the end of the slave and master cylinder, Brake fluid will be seen in the one with a leak. That said, in my experience, the cylinders are usually the same ancient age and if one is bad, the other is soon to fail. I always replace them both at the same time.

Get the short slave to hard line hose too.  I think I got the slave cylinder and rubber hose for $20 maybe?  amazon.com or rockauto.com, Beck Arnley is what I ended up getting.  FYI

Bleeding not difficult. Need a bleed tool or someone in the car to pump the clutch. Slave cylinder is on th passenger side of Trans. When you inspect it it will probably be a little moist. The slave cylinder doesn't hold much fluid so the slightest loss will cause gear selection difficulty. Maybe a 45 minute fix.