I think you may be referring to Cummins engine bulletin #3810340-02 dated 5/96. This paper discusses the possibility of molybdenum Dithiophosphate causing problems with some copper components within the engine and the use of copper de-activators in the oil to compensate. I no longer have this, so I am going from memory. Nothing was ever published or stated since that time that I am aware of.
I now have 2 PSD's using Schaeffer's 15W40 with moly and the analysis on my 01 are super and in the analysis section. Extremely low wear, and metals, ox, nit, soot etc.
Some oil company dealers still like to quote this old info as a revelation to sell their product. The knowledgeable ones don't and sell their oil on it's own merit. IMO