Connectivity issues are common in System 1 games, and I'd try addressing that first.

Try cleaning the metal contacts on the display's edge connector with a pink rubber eraser. That will remove the grime and tarnish. Also do the same on the MPU's edge connectors.

The next low hanging fruit would be to check for cracked solder joints on the displays and PCB. Then, if there are still issues, repin the connectors. And finally, troubleshoot the number display logic.

Not having owned a system1 I don't know what chip controls those, however that segment problem is likely due to a bad chip leg on your MPU. Also you said you were new to owning so when you check the displays by removing them don't forget to turn the machine off each time you disconnect a display and re-install it or you will blow those chips. Look at your manual if you have one and locate what chip drives your displays and I think testing will uncover bad legs.

Follow what Force has told you first and if it continues look at those chips as that looks to be a segment problem......which could have initially may have been caused by removing the displays and reconnecting them while the pin was on.

The circuitry and chips that drive the display (through digital logic) and determine what digits/segments to light up on the display. For (most) Gottlieb displays, there are two chips on the display PCB--one is responsible for digits, the other for segments. On the MPU, there is a a cluster of chips that are responsible for sending the instructions to the display PCBs.

https://www.pinwiki.com/wiki/index.php?title=Gottlieb_System_1#Display_Problems