1997 Mercedes Benz 320e where do I

The transmission fluid on this vehicle is filled via the dipstick tube at the right rear (passanger side) of the motor. It will ususally have a black or red cap on the end of the tube. There will be a small plastic lock you will break the end off and then push the remaining piece through. Remove the cap and fill with a funnel. Note that most MB models do not have a transmission dipstick. You can purchase one from most dealers. Also make sure to check fluid level with the trans at full operating temperature with the motor running.