There are a few ways to seal the space between two surfaces. When any object gets assembled, it leaves a gap between the joining parts that may or may not be visible. That only becomes an issue when that specific part is for holding a substance or hold pressure. In a vehicle, there are many parts of the engine that have fluid and pressure.
There are different types of gaskets used to create a seal for those parts. Some of these gaskets consist of rubber, cork, or bonding material. These gaskets can withstand high levels of heat or extended periods of engine combustion to support engine operation. Over time these gaskets can become worn or broken down and will need to be replaced. It is a more cost-effective and shorter process to change a cork gasket than rewelding two parts together. The gasket is a vital part of any vehicle.