Windshield seam sealer? What to use.

On my B body, I pressure washed out the channel around my windshield, and rear window, with the trim off, and was left with what seems like factory sealer or putty of some kind.

What's the best way to encapsulate, or reseal this gap/seam? Was contemplating masking it off and using some kill rust in there.

I eventually have to reinstall the trim and clips for that.

Thoughts?

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