Clutch shaft siezed where it passes through the alloy cover (Wok) common, you lift the clutch fully and the arm wont return due the shaft tight in the alloy, you let the pedal return master cylinder takes another stroke of fluid and you try and push it down - Hydraulic Lock
Unbolt the slave cyl to confirm its not siezed
Look at the shaft and if the 2 overthrow nuts are touching the alloy casing then its siezed, plus gas and let it soak in and if that wont free it then tap the alloy casing there is spring pressure from the diaphram pushing against it. If the arm refuses to return then its time to remove the clutch cover and disassemble, clean and lubricate