I recently removed my old front bondo queen fenders on the '56 Power Hawk and neither of 'em had the rubber gaskets that were supposed to be between them and the cowl.
I have no reason to believe that the left front fender was ever removed since the fiberglas repair to a rotted vent housing was still intact.
The left front fender was definitely replaced during the 1967-68 time period as the original was "Swiss Cheese." I was working overseas at the time but my mother handled that for me. The replacement fender was still in pretty good shape and had only one small rusticle beginning on the backside of the lower rear.
About the gasket issue... Ya' suppose that some cars escaped from the factory without 'em?
JT