[moopups]

In that the clutch works with the other gears, it is unlikely that clutch its self is the problem. The transmission must be removed to change the clutch, which allows oppertunities for linkages to get bent or out of adjustment. If this were a colume shift I would look to linkages, but I have never seen a 5 speed on the colume. I would suggest you take it to an expert and have a look at the bottom portion of the stick itsself, where it is out of sight inside. There could be a burr or normal wear on the stick or with the internal shift slides. There is also the posibilities of a bent shift fork caused by rough handleing, fairly easy to fix if the trans is a top loader, meaning there is a removeable top plate that can be lifted out.

 

[moopups]

Yes, a leak in the pressure end of the slave cylinder can cause the problem, because the piston that pushes the throwout bearing can suck back in air, because it is sealed at the sides. This would cause air to be in your fluid area which when compressed will fill a space made by absent fluid. Fluid does not compress, but air will many tines smaller that atmosphere volume. Set in the vehicle with it running and 'pump' the clutch, same as you would when bleeding brakes, now try putting it in gear; if it goes very easily or normal, the problem is obeviously the leaking cylinder.