Pump the rear differential oil into a suitable receptacle and remove the differential. To reinstall the 188L/188LW rear differential be sure to remove all of the fasteners, clean the sealing surfaces of the cover and the differential housing before installing a new gasket along with the cover in the reverse manner used in order to remove this assembly. For the 215L/215LW rear differential, follow the same steps: this requires you to unscrew the fasteners, clean the sealing surfaces, put in a new gasket for the cover and secure the cover in reverse manner as you removed it. And last, but not least, add more oil to the differential.