Remove the intermediate shaft sprocket. Drill two small holes into the existing oil seal, diagonally opposite each other, and thread two self-tapping screws into the holes. Using two pairs of pliers, pull on the heads of the screws to extract the oil seal, taking care to avoid drilling through into the seal flange. Alternatively, unbolt the flange, remove the inner O-ring from the inner groove, and press out the seal. Clean out the seal flange and sealing surface of the camshaft with a lint-free cloth, removing any swarf or burrs that may cause leaks. Lubricate the lip and outer edge of the new oil seal with clean engine oil, starting it in its housing by hand with the closed end facing outwards. If a seal fitting sleeve is being used on the ADR engine, do not lubricate the oil seal. Use a hammer and a socket of suitable diameter to drive the seal squarely into its housing, ensuring the socket bears only on the hard outer surface of the seal. If the flange has been removed, renew the O-ring, refit the flange, and tighten the bolts to the specified torque. Finally, refit the intermediate shaft sprocket.