Car's nowadays were really built with a certain projected lifespan. They intentionally design and built them for us to change parts or the whole cars after these xx years. Best example is our cooling system and now lately cylinder head cover, intake manifold with this plastics materials. Their premise is to reduce weight but the truth is they knew that after the defined lifespan of the machine this will be replaced. Plastics overtime tends to be brittle specially if expose constantly to high heat. Some cars was also poorly designed, where the exhaust manifold is even facing the Cooling system, ideally the exhaust manifold should be near the firewall.