If I'm not mistaken that is the vacuum line to the EZL. The EZL automatically adjusts the ignition timing. A small piece of rubber hose will repair the break, and will allow a degree of flex the brittle old line no longer has. Just lube the small hose with WD40 and slip the ends of the broken line into the hose.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.