Replacing the nose seal doesn't always stop an oil leak from the nose of the Sierra diff(presuming thats why you're changing the seal). Phil at R+R advised me as follows: When the flange is off, chemically clean the splines and the flange with brake cleaner and reinstall the flange on the splines with a liberal amount of RTV. Cured my oil leak that persisted after changing just the seal. Undoing the flange nut is best done with the diff out, undone with an air gun at a garage or ATS.