A recent development has been occurring throughout the diesel world. Folks engaging in oil analysis of their engine oil for newer engines have been seeing sporadic increases in copper in their used engine oil analysis. Most new diesel engines have oil coolers - inside those coolers is a network of small honeycombs plated with copper.
The zinc dithiophosphate used in many engine oils as an anti-wear component that will leach the copper. It won't hurt you per se but it does monkey up the oil analysis results making you think that you could be getting wear from valve train bushings, wrist pin bushings, cam bushings, thrust washers, governors, connecting rods bearings, valve gear train thrust buttons.
Here is a pic I just took - about 40X magnified. You can see the copper. Sounds simple enough but the OEM (Izuzu for GMC) had no clue this was going on. Even more surprising was the lead I have been seeing leach out of Cummins engines. Thats a whole other story.