I used this product called Ospho once when I was a kid, was pretty nasty stuff, but basically stops the rusting process, could look into it for inside of groover box.
Probly just Rustolium for the lid and outside of can.
In general, it is always best to get rid of all the old rust and crap first, the better job you do prepping, the better your paint job will be, whether it's a car, house, or groover.
A lot of times I just spray over everything though, because I'm a lazy boar, and run out of time!
We can't always agree, but we can still be civil to each other.