727 Servo Leak?

Since the reverse servo uses rubber seals and the KD servo uses steel sealing rings one would assume that the rear servo should seal up somewhat better. Even with that in mind I've never noticed much difference in how hard they apply when air pressure testing but I never use high pressure. Usually about 40 lbs is all I use. Do you hear air leaking from the KD servo when applying air to it? A very slight amount of leakage is normal but you don't want much leakage. How much air pressure are you using?

Also keep in mind the springs used in each servo. If there's much diff in the spring rate that will affect it.