Brownell's Alumahyde II. This stuff would provide some additional protection for subsequent cleaning activities. I've gotten gun cleaning 'stuff' on painted surfaces before and it just gums up, wipes off, etc. If I was going paint my rifle, I'd use this stuff.
From the description: "After full cure, Aluma-Hyde II proved solvent-proof to all but the most aggressive, copper-removing bore solvents. Aluma-Hyde II is formulated with a hard-curing epoxy base that contains additional, high-density pigment for a durable finish that sticks to all properly prepared aluminum and alloy surfaces, steel and plastics - it’s great on synthetic stocks."