Hey guys. For about a few months now, I've noticed a stain around the center cap of my rear wheel showing up every time I wash the car/wheels. I thought is was just dirt/rust coming from the hub, but now I'm just not 100% sure. There was a big storm that rolled through the other day and it looked worst than usual, so I took the wheel off. I can't tell if water somehow got trapped in there and started rusting or something leaking. I don't see any liquid though, so my first thought is just rust. What do you guys think this is? I want to get an idea if have to bring it in to a shop or not. Thanks in advance. Here's what it looks like.
