I used to be a TRUE believer in synthetic oil,but not anymore!In the last couple of years I have changed alot of differentials because the manufactures put this stuff in.It doesn`t matter the make Dodge,Chev,or Ford,I`ve done them all.The synthetic oil doesn`t stay on the gears,if you take the cover off a diff that has regular gear oil,it is still is on the gears.If you take the cover off a diff with synthetic,it`s like you washed the gears off.The point I`m getting is,everytime you take off,the bearings are dry,and can cause failure.By the way the diffs I had trouble with were NOT abused,all highway driven and had under 70,000 Miles.