I have an og Genesis / Mega Drive controller, but some of the buttons aren't working. I took a look at the PCB and my guess would be that it's either oxidisation or corrosion on the contacts, but I don't know where to go from here.

I tried cleaning it with a toothbrush and isopropyl alcohol, and when that didn't work I tried wd-40 contact cleaner. Neither seemed to have any effect on the brown bits.

Does anyone have any advice?