You both are correct. I should have qualified my comment. I wouldn't use oven cleaner on aluminum or an aluminum alloy, nor on a Parkerized finish (but it just doesn't look like Anton's gun has any Parkerizing on the areas that are yellow. I still think someone put some varnish or baked oil on metal that had been put to a wire wheel.)
I will confess, I have used oven cleaner on the worst of all baked grease or oil situations when nothing else would work and I didn't want to go to a bead blast. When I used oven cleaner, it was applied with a tooth brush or fine steel wool a small area at a time and quickly rinsed off. Any area that might suffer discolouring was masked off. In the situation I had to use it, it worked. It's a last resort -- certainly not something that is my first, second, or third choice -- it's a desperation choice when all else fails.![]()