First, I work in a phone repair shop, I'm not trying anything illegal!
I have a Z3x Box at the work, and a S3 i9300 myself.
A friend with another S3 at 600 miles, and has lost his EFS. I already told him to make a backup, but unfortunately he had it on the internal SD. After a bad ROM flash he had to use a PIT file for flashing a stock rom, and that he wiped everything.
His EFS folder was blank, no nv_data or anything.
With the z3x, I tried putting his imei and S/N on my EFS, then doing a backup and sending that copy to him (obviously I restored my phone after that) but it didn't work.
So, I'd like to know if there's any way to repair or regenerate the EFS with a working phone as base, without having to send the phone