Mobil makes their own additives but the below link pretty much tells that with newer Borated FM's the Borates plate and form a hard " surface " layer of an " Iron Borate " directly to the metal .
It's now my opinion that "most" of the Fe in Mobil SS analysis's is not wear metal from the cylinder walls or other cast iron components such as the camshaft .
With the large level of Boron in the SS motor oil and it's proprietary additive pack made by Mobil it now stands to reason why only the SS shows higher Fe than other motor oil analysis's . I don't really think it's too thin or a less robust motor oil at all . In fact it really does have large doses of additives for the cost .
Let's chew on this
http://www.rtvanderbilt.com/news_19.htm
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