Hi im new to this forum, being a mechanic and working on euro diesel engines. In my experience, the seals under the injectors between the cylinder head and injectors do leak gases from the combustion process. On the d4d engine these gases leak into the inside of the rocker cover producing a thick substance. The surface of the cylinder head needs to be clean and the injector base reemed flat , then the injector torqued down to specifications. My hilux is recently purchased and i will be checking valve clearances as often as i can and keeping a very close eye on any build up and or noise. Plus changing the seals as good measure. Every engine has a weakness of some type.
