Can't give a definite answer, but had a similar
problem with my Cordoba. Ended up changing the clutch cable and also the spring at the top of the clutch pedal. Cleared up the stiffness any how.
Other than that, I have no explanation as to why your clutch is stiff and creaky - unless the viscosity of the oil is weakened at certain temps because its a bit old.....?
Sorry for being no
help at all!
Ferret