Sega SG-1000 Corroded Cartridge

I bought a Lode Runner cartridge for the Sega SG-1000 while on a trip to Japan. Testing the cartridge back home yielded no results, just a black screen. Looking closer at the edge connector at the cartridge, the pins were completely black. Using isopropyl alcohol or contact cleaner on them would just result in black sot. I am wondering if they used silver plating on the pins, which could cause…