I once briefly discussed the possibility of the circle being a tire bead with Ric. One problem with the hypothesis is that the tire would not have deteriorated yet. To expose the bead, the rubber would obviously need to be removed, for example by burning, but that tends to also remove the plating, so the steel wires would rust faster. Another problem is how a tire might be removed from an aircraft. It couldn't be removed with the simple tools AE and FN had. If it got torn free from the aircraft by surf and currents, how did the rubber get stripped away from the bead?
I'd suspect the most likely source of a bare tire bead was a Jeep tire burned on the beech. This doesn't mean the object is a tire bead, nor that it is from a Jeep (or Lockheed). OTOH, it does reemind me of a (broken) tire bead, as seen in a junk yard after burning a tire. It would be nice to get a better view of it, with some sense of it's dimensions. The video has no scale.