IME it is unwise to introduce additives into todays wonderful quality lubricants
You probably would not think so if you were riding a 1979 motorcycle with high lift cams and flat tappets like I do. The idiots who decided that motor oil no longer needs ZDDP are basically throwing all the old engines off the cliff and significantly reducing the life of even the newer engines.
The idiotic thing is, ZDDP has been killed for the express purpose increasing the life of the catalytic converter from typically 100K to 150K miles..... but, that part only costs about $300 so I consider that incredibly stupid strategy when the side effect is to significantly reduce the operating life of the engine which costs about 30X as much as a catalytic converter.
Anyway, those of us with older engines have no choice but to put additives into "todays wonderful quality lubricants ".