Did you ever get this sorted out? Mine isn't back together yet, but I got it with this issue. For me, two of the score reels would not go back to zero. Manually cycling them to zero allowed a game to start. At the start of the next game, the reset motor would spin over and over. Same issue. When I had the head apart I took out each reel and took the mech apart and cleaned off all the dusk/debris in there.

You got yours in much better shape than I did. The cab paint was lifted and flaking off and the PF paint was turning to powder. Mine is behind other projects now, but all I have left is to get an overlay printed (striking out locally, but have a lead online) and apply and clear that. Put the top side back on and go from there.