Today we took a closer look at the PCB. One of the 7474 TTL for left player was sick. Replaced it, Game worked (...for nearly an hour). The the screen went dark

Fortunately no Monitor- but a small Video-Output-Issue. Ok, replace of the faulty 7410. Voila, works again. Now some little sound-hazard. The NE555 for second player died.
But after fixing it with a new one, everything is fine again. Lets see how long.
Same Problems with our Midway cabs. The Space encounter lost his 'tunnel', hmpf. Guided Missile got wrong vertical lines in the picture (Shifter-Problem)
Maybe these very old games from the Mid-Seventies are reaching their final days. I read somewhere, that the TTL-ICs have a limited lifespan of approx. 40 Years
Hopefully we can keep the old bastards alive for some more years.