international recommends an 85w140 but I cant find a full synthetic at that exact weight. would there be any detriment in using mobil1 75w140 instead? as far as I understand the 140 is the main number the other is flow rate while cold which may help it during winter a bit or is there more to the cold weight than that? would you recommend mobil1 synthetic or some other brand for this rear axle and diff? Thank You ahead of time for your suggestions and insights!