Just out of curiosity, which thread is that where you have found a possible solution? When I had this phone the top half of my touchscreen was not working, and I replaced the entire LCD+Digitizer assembly and it made no difference. The top half of the screen was not still working, so I was just wondering if I could do more for my device.
Regarding your issue, if I remember this right you do not need to downgrade in order to unlock your bootloader. Just skip the first step regarding the update of hboot and continue unlocking the bootloader, because the hboot has already been updated with the latest software version.