Don't overlook the hydraulics as a source of problems. The slave cylinder is mounted on the top of the bell housing, near the oil filter, with two 12mm bolts. Squeeze the boot to check for fluid leakage. Wet fingers mean a new slave cylinder is in order. Replace the cylinder and bleed the system.
Corrosion is a problem and the cylinders are inexpensive.
The slave cylinder is connected by a flexible rubber hose to tubing running along the firewall to the master cylinder. Check the hose for damage, but the hoses are not problematic. Sometimes the clutch master cylinder will leak externally. If it does, the fluid will leak into the driver's footwell area where it will be absorbed by the padding and insulation under the carpet. Always check both the master and slave cylinders for leakage if the reservoir is low.