On a long nighttime drive, there was some road work which left tar on the road. The tar had sprayed up on the sides of the car and on the wheels. I cleaned it all off with Turtle Wax's Bug and Tar remover, but the inside of the wheels still had a bunch of gunk in there. So, I put the car on jackstands, and got to work cleaning the insides of the wheels.
I think that I might have let some of the bug and tar remover sit for too long on two of the wheel insides, because there are now isolated brown discolorations in the wheels. (see pictures)



To try and fix this, I took a wheel off and cleaned it. I used the tar remover again, but that didn't do much. Then, I used a clay bar. For about half an hour, it kept picking up "dirt" each time I folded and used again. After about half an hour though, the stain was still in the wheel and I was tired. (P.S. those pictures are after the clay bar work.)

I haven't tried anything since then, and I'd like to ask the forum what I should do next.
I'm thinking take it off again and continue with claying. When (if) it comes off entirely, I should polish it with Nu Finish?

Thanks in advance.

 

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Pull the wheels. Start with clay, then try rubbing with isopropyl alcohol.
I'd also try an AIO product like Klasse AIO, Zaino AIO, Optimum PoliSeal or similar chemical polish.

If you have a strong adhesive remover (3M, xylene-based), you could try that, too.

I always keep my wheels coated with a sealant. Makes them easier to clean up.