found a hole in the upper side of the casing.. and its a old hole..
By the casing, do you mean the axle housing? Yeah, a picture would sure help. There should be a vent fitting on the axle housing, 1/8" NPT tapping. On earlier axles it's on the passenger side axle tube a bit left of the banjo section. If that's what you mean, don't JB weld it shut. If you don't have a vent, you'll get oil pushed out the axle seals onto the brake shoes. Not good.
