Re-setting grub-pc in ubuntu -
grub-pc as installed in ubuntu differs comlpletely from grub-efi.
From ubuntu -
Assuming the default grub package is installed ( and not grub2-pc )
Assuming that Mac OSX is on drive /dev/sda and grub-pc stage1 will boot from there -
This will reinstall grub files in ubuntu and grub bootcopde to the MBR of sda, and rewrite the grub-pc menu.lst. Hopefully it will correctly find the sda MBR.
Edit /boot/grub/menu.lst to increase timeout and comment out 'hidden menu'
$ sudo grub-install /dev/sda
$ sudo update-grub
Restart into refit and select the Partitoning Tool icon, update the MBR, restart again should give a TUX icon for grub-pc menu.
If anything fails, use grub32.efi to boot back into ubuntu to try something else.