I've run into that same situation where the hot exhaust did in the fuelproofing of the paint. I wound up covering that area with clear Ultracote. After I'd scraped and sanded and repainted of course. I would have preferred to paint clear epoxy over it, but couldn't find any at that time.

I also found that blue rustoleum matched one of the Ultracote blues almost perfectly. So I sprayed the aluminum gear blue to match the airplane. Two days later the paint was dry and seemed firmly attached. But when mounting the engine, old fuel dripped on it. Nope, it didn't do anything to the paint. But when I wiped the blasted oil off with rubbing alcohol on a paper towel, some of the bloody paint came off too. Lousy adhesion to the aluminum. I'd sanded before painting to remove oxidation etc, so I was ticked. First time I'd ever had a problem with that brand. I figured the plane would look like a garbage truck as soon as I fueled it and flew it. And didn't feel like sanding off the paint. So I covered the blasted gear with clear Ultracote. Worked like a charm. Turns out the airplane was a toy masquerading as a model airplane and lasted a VERY short time. That blue gear lives on however. Best part of the airplane it turns out. Of course, it was originally a retrofit to the junk gear that came in that ARF box.