How do I restore the оригинал GRUB2 after an update on the other Ubuntu install overwrites it?

I have в двойственный boot (actually тройственность with windows but that's irrelevant) with Ubuntu 12.04 [1] and another Ubuntu [2]. I recently upgraded [2] which май have overwritten [1] 's grub with [2] 's grub, ie [2] is top of the list and background цвет previously changed is back to purple. [1] being my main ВЫ, Пойдите like [1] 's grub back :(

Im well aware of the windows-ubuntu MBR issue that хан be fixed by reinstalling grub 2. Im just asking if therВs в simpler way when it's about 2 ubuntus. What could I do knowing that I have access to all ВЫ '?

PS: sudo update-grub in [1] isn't enough...