If it's just surface rust on bigger cast items such as steering knuckles, steering box, etc it's not really an issue; they leave them unpained as they figure they'll get scratched up & rust even with paint on them.

I was concerned myself when my steering box & knuckles and driveshafts got a coating of bright orange rust after my first water crossing, but 2 years or so on & they are a very dark brown & not even noticable anymore. I did pull my diff covers though & spray them with a rattle can of BBQ grill paint, & did the muffler too.