I have a 1997 Mercedes E 420. There is a slight ticking noise in the motor that sounds like a lifter is stuck or dry. I took it to the mercedes Mechanic and they said that one of my oil injectors went out and that there are alot of plastic tubes and peices that go to it. My question is where abouts is the oil injector and how do you test and change them so I can fix my problem ....... Thank you for anyones input !!!!!