There is a small return spring that doesnt do much. The real clutch action is the lever function of the pressure plate fingers which cannot be done by human hand. The insides would be really dirty from the wearing out of the clutch friction plate material over time, just like brake pads cause a mess on the wheels - the clutch plate causes a mess in the transmission housing.
It should not be oily. If its oily then you have a leak and need to correct that immediately. The oil can be from either the engine or the transmission.
btw your slave cylinder is quite rusty, put some silicone grease on the end under its boot and change the fluid in it. It would be like ink by now and pretty much useless as hydraulic fluid.