I've used it for 20 years. It's mostly phosphoric acid. I always rub it on raw metal and it dries to a dull grey and unless you handle things a lot will stay rust free for a very long time. Depends on how damp the environment is too of course. I soak small parts in it and it removes rust effectively. I use supermarket vinegar for larger things (takes a lot longer, but cheap) Keeps raw metal good, like this chassis: And this firewall and windshield frame: I would clean the firewall with a black Scotch disc, then similar to you except with the Ranex.