Condition of the bike aside, I’d sell that and look for one with the piggy back shocks at least, and less oil/grease leaking everywhere, and one that has at least been washed!
All exhaust will turn that rusty brown color if you ride it in the mud, never wash it, and keep letting it bake on time after time.
I couldn’t speak on the reliability of the Raptor as I’ve only had mine for a year or so, but I remember my dad had a Suzuki quadrunner when I was kid. We rode that thing everywhere, and every time we hunted. For decades. And I don’t think he ever once changed the oil in it, or lubed the chain. And she never ever once broke down. Of course he never rode it too hard, it was just a utility quad. I guess what I’m trying to say is that you’re really rolling the dice with whatever you get. You just have to hope it wasn’t ridden hard and take care of her.