My left side low beam headlamp is not working ('99 ML320). I purchased a replacement bulb, but need to know how to replace. I can't seem to get the plastic door (bulb access panel) off from the rear of the lamp assembly. On the right side it comes off with no problem. Should I attempt to remove whole assembly to gain better access to bulbs, or can I do this with assembly in position. The windshield water reservoir prevents me from getting the access I need to the bulb access panel. Thanks for any advice.

chris