I have a W140 with M104 engine.

I have a, what I suspect, a injector leak as the #5 injector have black oil all around the outside (just by looking) while all others are just dust.

I will properly get a mechanics to replace the injectors as its a 1992 car. However I read that there are other plastic, housing, hose, vacum that should be replaced as well.

Can someone explain what I need to tell the mechanic to replace?

Any idea of cost?

Thanks