69 Dart wing quarter window removal

Ok still having trouble is this what you meant, because I've had my hands in behind and there is nothing behind that plug. there seams to be some sort of bolt or screw holding it in. I could feel around but can't get it to move or get any kind of tool in it. bolt head id smooth with a hole in the centenaries if it. if it's an allen key I can't seam to find the right size to it's rusted solid. thanks

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