John,
40-310 is checking the adjustment of the rear level control valve. This is system is on a few specific models such as the 560SEL
.
Some info on your car would be helpful for you may not have this system.

In a nut shell the base weight of the vehicle is carried by the springs and then the hydraulics assist when weight is add to the vehicle. Unladen a 4 mm rod should slide through the level control valve arm and into a 4mm recess in the valve housing.

__________________
Paul