Preventing copper leaching in Internal Combustion Engine Oil Coolers

I work for a company that manufactures engine oils. Part of my job is to read oil analysis reports from the diesel and gasoline engines owned by our customers. The number of reports that cross my desk daily can be from zero to 150 and averaging about 30 reports. Over the last few years, I have noticed an increase in the amount of copper that is appearing in the engine oil whose source is the oil cooler. I am hoping that someone/somewhere has an idea on how to passivate the copper and prevent the leaching of copper from the oil cooler. If the copper is lost, leaks eventually develop and engine cooling products get into the oil which is not a good thing.