Why the drum brake Cylinder LEAK? and how to avoid this from occurring(02)

Why the drum brake Cylinder LEAK? and how to avoid this from occurring(02)

Image gallery: Brake Cylinder Leak

Rear brake cylinder leak?! : MorrisGarages Sinking Brake Pedal - Leaking Master Cylinder Cup Seals Why the drum brake Cylinder LEAK? and how to avoid this from occurring