Originally Posted by ICuaI
If you had searched I am sure you would have found the answer
Well, I too think that the bootloader-entering-combination for the updated 4.1.2 build is not well documented as I searched multiple minutes for it when I needed it
The key is: Power the phone on with Power + Volume Down, release the power button instantaneously as the phone vibrates and hold volume down until the bootloader is there.
This also works on any reboot: Just press and hold the volume down button shortly before the device starts to vibrate (see the green light) - no need to press the power button there.