PS3go finally released their downgrade update via the a9vg forum's!
Update: Confirmed this is working with factory / service mode now!
Here is how it works:
After degrade you can simply rename or delete downgrade.bin for ps3go and back to jb mode.1. Download this attachment, unrar it.
2. Plug ps3go to computer and file update.bin goes to ps3go root dir. (flashdisk not TF!)
3. Unplug it and plug it in again (this will flash ps3go to V10 core)
4. Send file downgrade.bin to the root of flashdisk to enable factory/service mode.
5. Use normail jailbreak procedure (press start and eject) switch on ps3
6. Turn off system via xmb. (Old model ps3 need to shutdown via xmb. New model ps3 will just go off itself!)
7. Power on and its factory / service mode!
Any question you can PM me I'd like to help out!
Official Site: GAMEBOX
Edit1 : Thanks member joshuab for the update info :
the first downgrade file caused the any hex function to stop working which has now been fixed in the second one and has been confirmed by danfozzzy in the thread
Theres V2 downgrade file available :