I remember helping my Dad (Body Shop Foreman) do this on several customers' cars back in the 70's. I remember him using A LOT more goo, especially between the gasket and the steel frame where the molding clips attach. Almost the whole clip(s) was covered with goo, and a larger diameter rope than that. I think the stuff he used was called "WindoWeld" adhesive or "Thykol." I think 3M made one and DuPont made another.
I don't ever remember one leaking.