[51 MERC-CT]

Original headlight bucket gaskets were made of either cork or rubber and were never meant to be an 'anti-squeek'.
They were just a gasket to prevent water and debris thrown up by the tires from seeping thru to the outside of the fenders.
If you ever saw a car that did not have the gaskets you could tell by the trail of water and residue under the headlights.
Anything with tar in it is most likely aftermarket or homemade.