Most likely shift rod bushings. Put the car on ramps and check them out. Can be done DIY.
Other candidate would be the neutral start switch.
My money is on shift rod bushings.
'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.