You're most welcome. The chip was of course going to eventually fail totally anyway, so flashing attempts would never have resulted in any change because of the partial-failure causing the bootloop. The only way to find that out for sure without JTAG testing the actual hardware is by first assuming a software problem and proceeding as we did (not even Garmin bothers with in-depth hardware testing for warranty-return devices these days). Unsurprisingly, often the faulty chip just gives up completely when a flash is attempted.

If you can be bothered, strip it for parts because the screen and battery are saleable on ebay, even the case might be worth something along with sought-after bits like the usb socket which can be easily unsweated.