I would think twice about adding an additive. Most oils are balanced pretty well so that the various additives play well together but there are instances where you can have some not interact well and end up precipitating. Not good for obvious reasons. There are several really good oils rich in the anti-wear additive ZDP or ZDDP. Look at the Joe Gibbs Driven products, Swepco, Valvoline VR1 to name a few. They have been developed with additional protection in mind.