One place I think these cars can leak is under the fender near the bottom edge of body. I am pretty sure that is where mine is leaking, since I have checked the battery area and corresponding area on drivers side, and just had the windshield replaced. I saw a w124 at a junkyard with the fender off and I was looking at that area, because that's where the water is coming from on my car. IIRC there are seams there and an area where the water sits and rusts the seam. My car leaks more when the car is parked flat or with the nose down. I also had trunk leaks, at the seams of the trunk lid front left and rt corner, and leaks in the seal gutter on the left side, mostly by the front of the trunk lid seal. There is still a small amount getting in that is perhaps the seam at the bottom of the trunk lid, which fills the trunk lid with water, and at the antenna. When they get this old there are a lot of places they can leak. The front sunroof drains are easy to see and clean...that wasn't my problem.
So my next step is to pull the fender and rustproof/seal that up.