Dismantling and assembling oil pump - AR27.50-P-0720-01A

WARNING: This page does not describe the selected car, but rather 42 other vehicles, including the 1999 Mercedes-Benz S600, 1999 Mercedes-Benz S500, 1999 Mercedes-Benz S420, 1999 Mercedes-Benz S320, and 1999 Mercedes-Benz CL600. However, it is still accessible from the selected car via links, so may be relevant.

Remove pump gears (22 and 23) from pump housing
Check radial seal ring (24), replace if necessary
Replace O-ring (25)
Lubricate pump gears and place in the pump housing. Insert pump gear (22) so that the chamfer (arrow) points towards the pump housing.
Use ATF oil

Fig 1: Identifying Pump Gears From Pump Housing
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Fig 2: Identifying Radial Seal Ring And O-Ring
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.