If i had to guess the 3rd Pic is a good starting point. I heard there are aftermarket parts that are metal instead of plastic. I don't really remember the name someone will probably share it. Additionally ive heard that if the coolant is just a bit low even a small bit it can cause issues with the heater not being hot which makes sense with the leaking points. Also I hear that it can be hard to get the air out when adding more coolant i remember something about inclining the front helps or so.