This exploit was publicly revealed in 1978. Worse, a couple years later, it was discovered that a certain sequence of inputs on the user (i.e., the *voter's*) side would cause an unmodified machine to roll ALL the votes it had tabulated to one party or the other at the user's choice, with no record this had ever taken place.
There’s reasons why the company went bankrupt within a couple years of these discoveries and the voting machines were taken out of service pretty quickly.
I get that people are nostalgic for those monstrous relics of the 50s and 60s, but they absolutely sucked for election integrity. We do NOT need to go back to them.
Best option I've seen so far is ScanTron based. Digital tabulation, but physical records and users can photograph their particular ScanTron if they want to make sure it doesn't get altered in someone else's hands.