Rereading your previous post, I see what you said about the filings you found. I kind of doubt it's from your turbo. I had a post on here about a poor oil report on a 7.8L Ford diesel and I had high copper, lead and iron. I found the turbo to be excessively worn but I would think if that were the case with you, you'd be seeing higher levels of copper as your turbo bushings would be wearing excessively at the same time as the turbo shaft. Have you ever had to do any repairs on your front gear train? When I worked at this truck shop for time, there was one truck that always had a lot of filings when you drained the oil. This truck had a gear that had come loose and tried to push out through the front cover, thus producing excessive metal filings/wear.