Isn't the windshield on an '87 E300D sealed with a sealant rather than a gasket? (similar to the W126) If so, I'm doubting the windshield leak scenario.

My bet is the condensation drain for the air conditioning. It is inside the center console, right next to the drivers' foot. The tubing is wire reinforced and foam covered. Over time the foam deteriates and with your foot constantly pressing in that area, it develops cracks and leaks. Usually noticable when your a/c is dealing with high humidity.

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Sam

84 300SD 350K+ miles ( Blue Belle )