You need to isolate the problem. Right before you are expecting your next good rain, tape your sunroof closed with blue painters masking tape, making sure to use three pieces overlapped on each of the four sides. Make sure it's taped very well. If you still get leaks, you've eliminated the sunroof. If not, you've id'd you problem area and you can start from there. If you pour water into the sunroof pans, can you see it run out of the drains, front and rear? You may have to angle the car to force it to go front/rear.

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1982 Mercedes-Benz 300CD
1982 Mercedes-Benz 240D - stick