I contacted Lucas about their 80w90 gear lube and they said no friction modifier is need for my LS rear end. Mobil1 synthetic 75w90 says it has modifier in it already, but a review says someone added more because of chatter and lost their rear end. Anyone used either of these and did you add modifier? Options? Experiences? Thanks all.

 

Royal purple, 50K, no addatives. No issues hooking up