The residue on the channel frame can be removed. The frame appears to be steel, which will rust quite readily unless coated with something, so you'll want to apply paint or some other coating. Depending on conditions, that can start pretty quickly once the metal is bared, so take that into account in planning your project.
As for what takes that residue off, I've usually sanded them. However, the residue has usually seemed to me to be something like dried varnish, as opposed to something waxy. If you use a solvent, definitely use it sparingly and be sure none gets inside the choke.
