okipoki,
On your Boeing, you will find rubber "P" seals installed on fixed structure of various sizes and lengths which are designed to rub against and provide an almost airtight seal between airfoil and structure irrespective if hyd sys is pressurised or not.
Have a closer look on your next walk around and you will see some of them, especially when systems are unpressurised and flight controls are drooping. Hope this helps.