While I would avoid the brakes, you can coat the exhaust. Doing so, you may have a smell for a few days while it cures completely, but it will not burn off. But, high temp paint would work on the exhaust as well. As for stuff not to hit with it, there isn't that much that you need to avoid. The only time it shouldn't be used would be with small electronic components that have moving parts. You can coat the engine, manifolds, exhaust piping, suspension, frame, inside of the body panels, etc, etc. I would recommend using the spray straw that comes with it to get into the tight areas between the mounting points for the suspension and other tight spots. While my testing has shown that the MPHD does really well at defending against rust encroaching under it, those tight spots would be susceptible to rust simply due to not being easily coated.