Flashing official firmware will not brick your phone, follow the guide and factory reset afterward.
On 4.3 you have efs v2 so can only unlock with a purchased code. You cannot go back to any firmware that would enable the old patch system to unlock.
Sent from my GT-I9300 using Tapatalk
Note: This quote doesn't automatically apply to everyone, decide for yourself if it might apply to you.
Originally Posted by justruss
What has this place become?
It's essentially a few people graciously answering the same repeating of immature, lazy, demanding questions from the masses.
Nobody searches. Nobody reads the first posts or titles of threads. Nobody even looks at posts a couple above their own.