Modern Vespa

I have a 2013 gts300 which is loosing water. After a long ride I will find a little puddle near front of leg shield. so I have stripped off glove box and foot cover taken on a long run can't see any leaks? Only thing I hear is a hissing from expansion cap lid would this be normal or is a new cap required

When looking today is see this covering on the expansion bottle pipe

The bottom right corner of the radiator has a leak(dirty water patch on the fins), take the radiator off and pressure test it. I have had the hose clamp leak on most of those hoses just use the screw type hose clamps. You may want to take the thermostat off and the water pump, easy jobs and then flush the system with a garden hose. replace with good coolant.

first thought is either a blockage OR pressure from the cylinder getting into the cooling system via a failing top or bottom cylinder gasket (my top gasket failed and I then got leaks from the coolant tank cap).

looking at the pics with the consistently brown hose from the tank and bottom of the radiator but not the hose going into the radiator makes me think blockage. remove hoses and radiator and check for blockages as srd0060 is suggesting.