Which hydraulic clutch part is bad?

My kid has a 5-speed 2005 Ford Escape. The pedal got super soft yesterday and shifting got very hard. Seems like a hydraulic problem. The master cylinder and slave cylinder are very accessible, and neither seems to be leaking. They share the brake fluid reservoir on this model, and brake fluid levels are good. Do these cylinders go bad without leaking? Any suggestions on how to figure out what needs replaced?

 

Internal leak in the slave cylinder?

Firewall or mount point of said cylinder flexing?

If both are easily accessible, when the clutch is actuated are you able to see movement on either the slave cylinder or the clutch? Do the thro lengths look appriciate if you have visability?