Had this with a Mitsubishi Shogun. A hydraulic clutch, the fluid had not been changed all its life. Did a fluid change in the normal way and bled all the air out of it at the same time of course. Pedal back to normal and as good as new.
Manufacturers recommend brake fluid changes every 2 years but people tend to forget about the poor old clutch fluid which is hygroscopic too.
Ron
Chicks Fan, November 2008