Sounds like the check strap seized. Between the hinges should be the check strap, may be under a rubber boot. Try oiling the strap and see if you can get the door closed. Inexpensive part and yes the inner panel needs to come off. There is a DIY article on how to replace the strap.
'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.