Wow, nice motor! The base gaskets are readily available….no need to make them. They are tough ones to make anyway, as they are somewhat complex and not very robust, in terms of just handling them.The o-ring inside the lower crank seal is also still available. Since 18s are prone to water ingestion and seizure, if it were me, I would replace that o ring. Just be very, very careful of the black piece, as it is EXTREMELY fragile, if pried upon.
Long live American manufacturing!