the hood hinges. I have run into and solved this problem on 3 W123's. What you have to do is get a snake--you can work just as easily from the spot that the drains holes connect into, which is the front tire well on each side, Either that or use a coat hanger and slide it through several time. These drain holes may be hard to find the first time. Maybe someone can post a picture or diagram. On the passenger side, follow the gulley where the hood hinge is about four inches forward , there is a hole in the side of the gulley. Right next to that gulley is the actual drain hole. Leaves and stuff get in there over the years...