With a forum name of "old school" you might disagree but if you already have 2 bad the other 2 might be right around the corner. I would get a complete new rottendog set and save the 2 good original ones you have for another machine. The rottendogs are really nice and you can hardly tell the difference. For good working originals your probably looking at $50 each. A set of rottendogs are $159.
https://ksarcade.net/rottendog-led-displays-system-for-williams-3-6-dis326.html