Like many others living in the northeast, my axle housing rusted out. I found a mint rust free replacement and plan on swapping everything over. I wanted to know what the best way to protect it from rust would be.
I don't know if I want to take a wire wheel to it considering the factory coating is still intact. Is there anything I can spray over the factory coating to protect it?

Thanks in advance!

Many products to choose from that will help protect it from the elements. I personally like LPS 3 but many on here like Fluid Film or even WD40, all will work good. Just coat it a couple times a year (and your frame , inside and out) and it will keep the rust at bay.

Boiled linseed oil.

Dont wire wheel it, use some 180 grit sand paper to rough it up. Then paint with something strong like roll bar & chassis paint.

Factory paint is garbage, it will rust at all welds. If it really is pristine with no rust I'd degrease it with POR degreaser then spray with rubbing alcohol to finish it off. Then spray with a black automotive spray paint. Don't use any of those tough monstaliner type paints since if they get compromised they will trap moisture and salt underneath and rust quickly. I saw a sad case of a cruiser with that. They thought they were protecting it from rust.

Then spray with an oil based coating of your choice. You could skip all the painting and go straight to the oil but since it's so clean it will be easy to paint.

Particularly pay attention to the diff pumpkin cover, that metal rusts really easy and it doesnt flake off. It just goes deeper and deeper.

Regardless if the paint is mint or you repaint it with whatever......Do seasonal coatings of a weapon of your choice, you'll need to do it before every winter season. A true salt belt warrior doesn't have their rig rot out cause they prevent it with diligence. A seasonal spray down takes less than 30 minutes.