my experience is with Mobil1 . I use Mobil 1 15w-50 most of the year. It has a Nominal Phosphorus Level of 1200 PPM of & a Nominal zinc Level of 1300 PPM. with those levels I have not used any zinc additive.
In the winter I use Mobil 1 0w-40. It has a Nominal Phosphorus Level of 1o00 PPM of & a Nominal zinc Level of 1100 PPM. With those levels I do use a zinc additive., Cam Shield
http://www.cam-shield.com/
unlike other zinc additives, the Cam Shield label provides a formula that can be used to tailor the amount used so you can arrive at a specific zddp ppm number.
After 43,000 miles over a 9 year period I have no measurable engine wear & no leaks.
http://www.mobiloil.com/USA-English/Mo…l_1_15W-50.aspx
http://www.mobiloil.com/USA-English/Mo…et_Engines.aspx
unless the Brad Penn oil is in the 1200 ppm range I would think about using some zddp additive with it. From what I have heard about it, it's a high quality oil, but somewhat pricey. I don't know if it's worth the extra $$$ over a Mobil 1 product.
If the Brad Penn oil is marketed as a racing oil, I wouldn't use it in an engine that is not going to be raced and subsequently disassembled after every few hours of operation.
Z.