I have replaced them without removing the engine. Remove your pulley /PTO clutch , drill a small hole into the metal of the seal , Install a screw into the drilled hole and use a claw hammer to pull out the seal. Use a section of 1 1/2 inch PVC drain pipe 6 inch long or longer as your seal driver to install the new seal . I have had to change a few sump gaskets on them . The gasket is not pushed out but was sucked into the pan. They sell a Dye to put into the engine oil that will glow with a black light to find the hard to find leaks.