Iron X and Iron X gel. It is basically a stronger version of Sonax, made not for regular wheel cleaning but removing baked on contamination without removing the finish. I think if you hit that area with a toothbrush and metal polish the finish would start to come off.
Detailed Image and Autogeek sell it. The gel will stay in the area for longer, the Iron X spray will hit the whole wheel. Sonax is good for maintenance.