Friction midifier and a mild AW additivee used when ZDDP is reduced to still give valve trian protection moly is also used aswell as other additives. Boron and moly are the most common used in delo I think. bruce
Boron is also used in Chevron Delo GL-5 gear oil instead of soft metal abrasive sulphur. That makes it suitable for almost all gear boxes using soft metal parts requiring GL-4 without any fear of damage.