Boeing Co. discovered that its largest supplier improperly drilled holes in a component that helps maintain cabin pressure of the 737 Max jet, threatening to derail delivery targets for its best-selling model.The latest issue for Boeing’s cash-cow jet isn’t a safety threat, the Federal Aviation Administration said Wednesday. But it’s another complication for Boeing as it speeds the manufacturing pace of the 737 family while dealing with supply-chain strains and the aftermath of a strike at Spirit AeroSystems Holdings Inc., the supplier that builds about 70% of the...