Headed overseas before Christmas, Pvt. George A. Posey wistfully spent his last few minutes in St. Louis yesterday at Union Station with his girl friend, Miss Margaret Scheer, 226 Fannie ave., Luxemburg, as the Southwest Hight School Choir strolled through the station singing Christmas carols. Posey, who had been stationed at the Army Medical Depot here, was off for Seattle and duty overseas.