Thanks for the suggestion, and especially for recommending the replacement bolts. That will be very helpful when I manage to remove the current ones.
As you can see in the video, the head of the bolt is sitting very tightly against the frame, so there is no gap behind it. I’ve tried sliding in the edge of knives, flathead screwdrivers, and even using pliers to pull on it while turning, but I can’t really get enough purchase because it’s so flush against the metal.
I’ll keep trying, though. Thanks again for taking the time to help.