10-4.

On my radar, is not only the groove, but the 2 sides of the channel, where it's metal on metal with no high points.

I have yet to get the wiki on whether all of the mag has to be sealed once cleaned. As it comes from the factory, whatever paint they use, they def used it on the inside cover. Can't recall whether the channel was raw or not.

For the inside, I was thinking of going on this direction.
Glyptal 1201 Paint - The Eastwood Company