I'm not sure if the adjustment is the same as on the 190's, but on the 300E the rest position of the wipers is adjusted from the front:

1. Swing down the wiper arm, away from the headlight.

2. Where the wiper arm connects to the motor shaft, there should be a small bolt.

3. Use a pair of needle nose pliers to loosen the bolt, adjust the rest position (you may have to swing the wiper arm back and forth to check the final position).

4. Tighten bolt.

5. Swing wiper arm back up until it engages the clip.

-anthony