Yes this is another crap design feature in the car, most decent cars have a dip stick in there to check the level, or at least let you fill to the top. To have the overflow running into the inner wing and leaking out of the car pannel joints is a bizzare idea to say the least! One day Ill cure this by fitting a proper overflow pipe like it should have in the first place.
Ill add it to my list!
Cheers steve