'64-'66 Abody Cowl-How did Factory Make it Water Tight?

We drilled away all the welds on the '65 Formula S cowl, removed the cowl. made various rust repairs, and now it's time to re-attach it. Using just spot welds, it seems to be it will be leaking here and there.

How did the factory waterproof it?

How does the crew here (who have experience) re-attach and seal the cowl?

Thank you.

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