I found out that I permanently modified my valve cover by overtightening the valve cover nuts on my OM 617. I found this out in a strange way two years after I had done it. While dropping the oil pan to bang out a dent from hitting a rock and to replace the oil pump strainer which was damaged from the dent I found a strange chunk of aluminum sitting in the pan. I looked around the lower part of the engine with a light but found nothing, mystery remained but suspicion was the valve cover. Then shortly after during a valve adjustment I found the part of the valve cover where the studs go through and meet with the valve cover seal was a match for the chunk of aluminum.