Replacing 74 Duster Tail Lenses

I had to pickup a new set of lenses and I'm trying to install them - thing is the originals used a gasket that is smaller and has some black caulking oozing out between the lens and the gasket. When I did a test fit there is clearly a gap that I probably need to add caulking too.

I'm wondering what kind of caulking this is and is there a trick I should be aware of when applying? The original lens appears like it came from the factory this way.

I've attached a pick for reference, thanks in advance.

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Author: admin