some (most actually) NES games are so damn grubby that NO amount of alcohol & q-tip scrubbing is gonna get it done. I usually do the initial heavy scrubbing with Windex, it works great. then clean all that off with alcohol.

I've had some near black contacts gleaming using Windex, it works okay on corroded contacts too. those require a bit more work. sometimes it takes about 20 minutes to get one cleaned right but it's worth it.