The containment ability of the GMC Seals and Gaskets is more than just for atheistic purposes. It is true that leaking gaskets and seals do make the appearance of the engine to look unsightly, but the oil and other fluids that leak out of areas they should be kept in also damage the surrounding components on your GMC engine.
There are seals and gaskets on every joint on the GMC engine and on the other accessories mounted on your vehicle. Each one is built with a specific purpose in mind by the engineers so the fluids can be contained in the most efficient manner.
The material the seals ad gaskets are created from are determined by the way they will applied to the application on your vehicle. Most seals are made out of a polymer or reinforced polymer depending on their placement and function. The greater the stress being applied to the place where the seal is to contain the fluid, the greater the need for reinforced fibers in it.
When it comes to gaskets, most are silicone, asbestos or cork. The ones located on the engine block, like the head and exhaust gaskets also have metal components in them for addition strength and ability to expand as the GMC engine heats up.
Since each application is different for every GMC seal and gasket, a great deal of thought is placed in their construction. This is why the seals and gaskets placed on your vehicle can contain the fluids for such a long period of time when in proper working order. If the fluids are permitted to leak out onto other components, they will negatively affect their performance and longevity.