Fix for corrupt efs on the Samsung Galaxy S3

TD:LR Get back to Stock ROM for your country and then restoring EFS the backup will help in getting back your IMEI.

1. Stock country ROM + Rooted if necessary
2. Any EFS backup
3. Same tool used in (2) to restore it back.

Currently I was 4.3 XXUGML2 ArchiDroid V1.7.3. Faced a lot of issues with any 4.3 ROM i tried. So I though I will go back to 4.2.2 OXAME7 [EFS v1] which was real stable for me. I flashed 4.2.2 again via Odin. After successful boot I had lost my IMEI where the code was generic 0049***. Here are the things I tried to do:

1. I had efs.tar.gz file which I had created when I was on 4.2.2 before flashing 4.3 with help of kTool. I tried to restore the same with help of the same app, but that did not work at all.
2. I had made EFS backup via custom backup and restore of Philz CWM Recovery. But that backup was in Internal SD. After I had flashed 4.2.2 from 4.3 with Odin the internal was completely wiped. So I had lost my 2nd and final alternative backup.
3. Tried to flash XXEMG4 modem which is actually EFS v2 modem, but that too didn't solve the issue.

Now why did this happen?
I am not sure, but my guess was that this happened because the 4.2.2 ME7 ROM had EFS v1 path whereas the 4.3 ROM was EFS v2 path. Any other possible reasons?

The Fix
As a last resort
1. I downloaded the Stock ROM for my country (India) which is XXEMH4 via odin --> No IMEI yet
2. Tried to restore the EFS via kTool again.
3. Profit + hefty amount of relief.

It was a great relief for me to see the IMEI back and thought of sharing it here. Hope this information will be helpful to others. 

credits - xda-developers