MYRTLE CREEK — When the city began looking for someone to replace City Administrator Aaron Cubic, who left in May to become Grants Pass city manager, Sean Negherbon wasn’t looking for a promotion. Negherbon, who has worked for the city for all but two years since 1998, had moved up from water plant manager to public works director and was satisfied. He never considered applying for the administrator’s job until Acting City Administrator Dale Shaddox urged him to think about it. Shaddox spent his career as city manager in Brookings and three California cities. Since retiring in 2007, he has …