Brian Legge, check the screws at each end of the focus distance plate just above the focus lever.The holes that they go into are tapped clear through to the film chamber. When refurbishing an Autocord, I had the hardest time figuring out where my light leaks were coming from until I saw that the plate was off and I checked out the screw holes. Maybe one of them fell out or is loose?
Some day I might fit a Planar or Xenotar 75mm f3.5 to an Autocord since those lenses tempt me to the Rolleiflex. But the focus system on the Autocord is just so easy and well-done, I'd dread going back to knob focusing.