Replacing a light bulb in a Mercedes Benz E320 is generally simple. The headlights are accessible from the front hood and the rear lights are accessible from the trunk. The side marker lights are different.
The side marker lights are built into the front bumper and the bulbs are replaced by prying the side marker lights with a flat screw driver from the front side of the light. The whole light assembly is held in place by plastic prongs in the housing. Gentle leverage is sufficient to dislodge the fixture. The base of the bulb socket is detached from the lens by unscrewing counterclockwise.
The following image shows the bayonet-base bulb in its base. It is ready to be attached to the lens by screwing the base with a clockwise twist. When the base is properly attached to the lens, replace the light assembly into the bumper cavity and press gently to snap it into place.
The bulb cost $3.31 Dollars.