Clearly nobody could have foreseen that someone would mistreat a SOLAR PANEL by leaving it out in direct sunlight for an extended period of time.
This use case is clearly well outside of its intended design parameters.
The interesting thing is that this has been getting most of its sunlight filtered through a car windshield, which should actually block most of the incoming UV (around 95%), which makes me wonder how fast the mounting brackets would have disintegrated if I had left it out in actual direct sunlight.
I also forgot that the frame used to be anodized black (or maybe dark brown, it's hard to tell). It had faded so gradually towards the bronze color that it completely didn't register in my mind.
The good news, however, is that these brackets aren't actually critical to my application, and in fact I wasn't even using them at all.
I will not miss them.