Zinc
I used Spectro motorguard, conventinal 10w40.
Their bottles are clearly marked 1800 PPM of zinc and phosporous where the Brad Penn, Joe Gibbs and valvoline VR-1 don't.
Also the spectro stuff is mixed in smaller batches not manifold large quantities thus ensuring quality concentrations in their batches.
Each bottle is labeled with the batch # they came from.
http://www.performanceoilstore.com/proddetail.asp?prod=R.MG14