After much trial and error I finally found a method that allows us to have a fully functioning MM (6.0) which is rooted and has a working custom recovery.
Be sure to Follow the instructions very carefully. I do not write these tut's so you can skip parts of it or ignore what is being said. If you fail or do not understand a certain step then simply ASK!! All steps are critical for success.
Choose the download (at the bottom of this post) which is for your device ONLY do not flash others!! thinking it will work.
If you do not see your C4/C5 device listed then please upload the MM boot.sin only for your device stating the model and device number (C5 Dual E5xxx)
Please use a quality upload site with no spam like Mega, OneDrive, GoogleDrive, etc etc
First you need to get back to a full clean factory 5.1 this is called "Rolling Back" and to achieve this we will first need to use FashTool
You must of already done an official Sony bootloader unlock before on LP or MM and used the exact same FlashTool with the unlocked bootloader at least once.
To explain FlashTool takes a copy of your Unlock codes and TA by default and saves it then the next time you use FlashTool You simply hit BLU to lock or unlock the bootloader.
1. Using Flashtool lock your bootloader and then flash as much as possible of the old 5.0 firmware.
For those who's devices never had 5.0 then see this post here http://forum.xda-developers.com/show...3&postcount=33 which explains that you need to flash the earliest version of 5.1 possible!
2. After this you can use the “Update” function to receive the OTA update which will put you on 5.1
Thanks to @Kenzi BNH for this tip.
2a. If you have followed THIS small tut and used Xperia Companion tool to achieve the same state then that’s also fine. (Note: It has been reported that the latest version of Xperia Companion Tool no longer does incremental updates and will now put you on the Latest Android version for your device but the above way via OTA's still works)
Note: The above methods are the ONLY ways to achieve this. Thinking you can skip or miss the above will lead to a failed root You have been warned!
3. Now using FlashTool Flash only the MM boot.sin, oem.sin, userdata.sin and system.sin which is made for your device.
Do not flash any other parts for now as more testing needs to be done with other partitions.
4. You should now reboot back to system and check all is working as it should.
(Note: I had to manually download/set my carrier's apn as the MM apn.config is in the oem partition which I did not want to flash until I had got root)
5. When you're happy all is working go to your Internal and external Sdcard and rename any “TWRP” folders to oriTWRP
6. Now copy the Exxxx-boot.img and SuperSU in the .zip (files attached below) to the root of your Internal Sdcard.
7. Using only FlashTool UNLOCK your bootloader.
(NOTE: It is very important that you only use FlashTool for this procedure as unlocking the bootloader via Fastboot seems to put a FLAG in one of the partitions (I suspect secro or sec-cfg) thus causing the issues with LockScreen & Security FC's in MM.
8. Now you need to re-flash TWRP recovery via Fastboot “fastboot flash fotakernel fotakernel.img”
The recovery's are in this post http://forum.xda-developers.com/show...93&postcount=3 under the heading “DOWNLOADS HERE:”
9. IMPORTANT: After you have flashed the recovery manually reboot to the recovery using the buttons.
“Press and keep held the Volume Down key (-)
Now Press and hold Power Key until you see the Sony Boot Logo then release the Power Key only.” When the recovery boots It will Ask if you want to keep the the system Read Only YOU MUST SAY YES
10. Now from the TWRP menu select install and select “image” find your custom Exxxx-boot.img and flash it to “boot” Then go back to the Reboot menu and select “recovery” Make sure to choose Read Only option again on reboot.
11. Now select install and flash the SuperSU after it has done and hopefully without any errors reboot to system.
12. If everything has worked you are now rooted and can carry on as before.
13. Rename your "oriTWRP" folders back to “TWRP” note That you can now mount the system read write again by using the swipe button if TWRP asks you.
14. Give THANKS, feedback and any suggestions.
IMPORTANT UPDATE NOTE: Firmware versions dated 2018 need the boot.sin repacking due to changes Sony made so if you are using a 2018 firmware you will need to upload the boot.sin giving full details of the device Model, firmware version and date. Without this info I will do nothing and ignore your requests also use a NO spam upload site like google drive, mega, etc etc
Be sure to check the download name as I have had to update all the links.
For testing the method.
WARNING Some people are recommending using a later FlashTool version than what I recommended. So just to be clear I DO NOT RECOMMEND USING ANY OTHER VERSION than the one I have linked above.
The FlashTool Website also says not to use it so you have been warned.