Hi David,
I gather you created a separate /boot partition?
Suggest you try the following -
Boot into the Mint OS distribution that you wish to configure GRUB2 from.
Run -
sudo /usr/sbin/update-grub2
This runs a script that in turn runs grub-mkconfig on the /boot/grub/grub.cfg file.
See man update-grub for details -
http://manpages.ubuntu.com/manpages/...te-grub.8.html