Stiff brakes after overnight

[SandStorm]

Having brake issue. After the wild cat is left sitting for a few hours, when returning to it, the brake pedal is hard as rock.
Only eases after starting the engine. Meanwhile I detected a leak around that yellow rubber cap in the cap from the brake reservoir. Can be that the culprit?

 

[zinc2000]

Firstly, you will find most cars will have a solid pedal until you start the engine, then the pedal will drop, perfectly normal, ignore it!!!
Leak around reservoir means to much fluid, maybe syphon some out until the level is back to where it should be

 

[oilburner]

Servo assisted brakes, they work off the vacuum in the inlet manifold so only work with the engine running, last car I saw without a brake servo was a 1980 Austin Metro 1.0

 

[SandStorm]

While some resistance is expected, it's not normal after some hours the pedal being so hard you can't press it. Like if you had pumped it up several times.
Neither my 2003 fiesta mk6 or 1987 orion mk2 do this. I didn't had this issue on my puma.
About the fluid, is at max mark, but will remove some, thanks