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Olds didn't use foam gaskets, nor did they use sheet metal screws to mount mirrors, so your parts are not OEM. The factory mirrors used screws that fit into those large keyhole slots in the door and used a molded plastic gasket. Your parts are aftermarket.
The correct manual outside mirror package for the 68-69 cars is P/N 231265, which is the number for the mirror assembly including gasket. It is not the casting number you will see on the underside of the pedestal. It looks like this.
The casting number on the underside of the pedestal is 400543.