Thanks
... ET wasn't the only working one, don't be scared!
3/4 were still working straight out of storage, and after some cleaning I was down to 5 unresponsive ones. After much more cleaning, I have only one Activision freeway (some sort of chicken run / frogger clone) that still isn't working. I opened it up, solders are OK, connections are clean, still nothing. I will try again another time. Maybe I need actual contact cleaner instead of alcohol.