Joined: Jun 2009
Posts: 2,242
Likes: 1,660
From: PacNW
Bikes: Dinucci Allez 2.0, Richard Sachs, Alex Singer, Serotta, Masi GC, Raleigh Pro Mk.1, Hetchins, etc
that derailleur is 40+ years old and they were only marginal back in the day.
Looks to me like the tension spring is pooched out. Slack. Kaput.
I'd suggest a new RD. Get a mid range shimano off ebay for 20 bucks.
Caution - you may have a french threaded dropout. Solvable problem
/markp