On the passenger side of the trunk under the plastic insert I have a puddle of water. I was wonder if anyone might know where this water is coming from and how to resolve this problem.

water leak in trunk of 1983 240D
 

There is a drain(it's a rubber fitting) that is probably clogged up. Take a screwdriver and push through it. As for the leak; dry the trunk out real good and then take a water hose and go over the trunk with water. If this doesn't work, have someone with a flashlight get in the trunk and flow water over the trunk. Good luck.
Bill Lewallen Lexington,Ky.

I usually just reach under from the side of the car and push around the four petals with my finger and this will cause it to drain.

Good luck,

My 123 leaked at the rear window. Many 123's also leak at the taillight assembly. My wife and I stopped to look at a 1979 300d at a car lot and when we opened the trunk both wheel wells where FULL of water. We didn't even take it for a test ride. This is a very common 123 problem. Good luck and happy holidays, Jay