Here is a link to my drop box that has software 1.3 which should get you access to firmware 5.12 ... I think
never tried this before so let me know if it works or if there is another file you may be missing
Ps I have not had any bad issues with one controller on 5.12 (I always run a separete BEC for the FC and for the gimbal... I don't trust their PMU) however on my other controler it flies like SH*T comparatively so it's the brain...