My 2E used to overheat on hot summer nights, and when it did, it would behave very strangely. That's why clip-on cooling fans were a very popular accessory. And for years, someone (Jameco?) used to sell a replacement power supply with built-in cooling fan.

It's also possible that our good friends, the electrolytic capacitors, are shot. That wouldn't be far fetched if the system was boxed up and sat idle for 2 decades.