Im getting ready to change the diff. oil in the front and rear, and was wondering if anyone knows the correct size o-ring to use for the fill plug. I'd like to have it ready when the time comesbut I cant seem to find it anywhere. Alsothe work shop manual says to use 75/90w, but the sticky calls for 80/90w. Any recommendations? I did see gear oil made by Lucas and that was 75/90w. I'd like to know what most of you guys are using out there,that seems to be best for our trucks. Thanks in advance.