It always best practice to replace rubber return lines during any major system disassembly. These hoses often get brittle and have a tendency to wear on high mileage vehicles. Although the exterior of the hose may look fine its not uncommon to see degradation on the interior of the hose. We see lots of these hoses get damaged during service or during performance upgrades.
This is an actual OE Regulated 9th Injector return line. This portion of the the return line does not include the drivers or passenger side injector returns.