Auto parts maker Delphi Corp. is free to move ahead on its plan to offer thousands of hourly employees the chance to retire, a bankruptcy judge ruled Friday, marking a key milestone in the company's effort to tame staffing levels amid falling production. The ruling allows Delphi, one of the world's largest suppliers of auto parts, to pay as many as 13,000 hourly employees to retire. Based in Troy, Mich., Delphi filed for bankruptcy protection in October and is trying to shed what it says are increasingly unsustainable labor agreements that have left it overstaffed and saddled with costly benefit...