check out this post: https://pinside.com/pinball/forum/topic/home-for-the-gottlieb-sys1-sys-80b-guys-yep-i-guess-it-a-club/page/75#post-5701968
That is segment C. I think this means Z2 is failing. Z2 is a UDN6118 and looks like they are not cheap. There is a way to test this chip here: https://www.pinwiki.com/wiki/index.php?title=Gottlieb_System_1#UDN6118_and_Other_Display_Logic_Chip_Failures