ummm, ur servo could probably be wearing out or getting old. U could try putting a return spring(something to help pull it back like a rubber band or sumthin) but then the servo might not be able to pull the brake at all.
Mine does the same. I think it's to do with the spring in the servo saver not being tight enough. I read somewhere, to clamp it into a tigher radius with some pliers and see how that goes. Personally, I am going to buy a new one from TowerHobbies.