Oil??? Do you mean you change the brake/clutch fluid regularly? (Brake fluid is not "oil".) Is the fluid clean looking?

Most of these older cars have probably had indifferent brake/clutch fluid changes over their life, so at this point the hydraulic components are probably living on borrowed time.

A bad slave cylinder often is indicated by clutch drag or lack of release. I think the clutch pedal sticking to the floor symptom is more indicative of a bad master, but the slave is probably not far behind.

Duke