It looks like behind the vented area there is a seal up top, but it seams to be like one that just slips in..it seems like some sort of foam..It is in the general area of the leak and is not pliable..I will get up some pics...

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1976 300D
190,000 Miles
Colorado Beige

1975 300D
Parts Car
78,000 Miles
Rustbucket
Also Colorado Beige

1984 190D 2.2 (Dad's)
156,000 miles
Champagne Metallic Clearcoat