Delo Silver SAE 40 = 0.06% (600 ppm) from their web page https://cglapps.chevron.com/msdspds/PDSD...Format=PDF so it is not that high really 
Delo 400 Multigrade = 0.15% (1500 ppm) from https://cglapps.chevron.com/msdspds/PDSD...Format=PDF now this is a good level
From reading up on oil shear and modern oil stability I will stay with Delo 400. It has a very good level of ZDDP and I have had good experience with it. The only negative issue could be that due to a the high detergent action this oil has, it may dislodge or dissolve deposits in old engine and could cause leaks on old seals. My engine is still fresh so I haven't had any issues.
Delo 400 Multigrade = 0.15% (1500 ppm) from https://cglapps.chevron.com/msdspds/PDSD...Format=PDF now this is a good level
From reading up on oil shear and modern oil stability I will stay with Delo 400. It has a very good level of ZDDP and I have had good experience with it. The only negative issue could be that due to a the high detergent action this oil has, it may dislodge or dissolve deposits in old engine and could cause leaks on old seals. My engine is still fresh so I haven't had any issues.
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