Ok next start a new game, and go to the score relays and with a screwdriver touch the tip of the screwdriver to the side of each set of contact blades so you touch both blades at the same time. One of the sets of contacts controls the score reels. Make sure you are only touching the screwdriver handle only while doing this or you'll get zapped.
Hmmm...... After thinking about it the relays might be the problem. It's possible the wipers on the steppers are dirty. I'd have to look at my game to see what actually controls the scoring.