The clutch master cylinder will be at the other end of the hose. That or the slave cylinder is likely the source of the leak.
The master cylinder could be leaking inside the firewall; usually behind the carpet.
I would doubt the reservoir would leak unless you could see a crack.
The mess on the firewall could be from the PO spilling fluid refilling the reservoir.
Check the master and slave cylinders for leaks.--
Embedded Systems Consultant,
SHDesigns home - DIY Welder