Rolf was on the track. The problem was definitely due to the 1st Ball Relay but only because that relay was not holding on when pulled in. Here's a schematic snapshot:
IMG_1771 (resized).JPG
You can see the J relay coil in the center. That's the 1stBall Relay. It passes through the score reel reset switches then runs through a switch on the SB2 relay. That switch does other things and those were working so I ruled it out. At first I was focusing on the J relay switches themselves but they all looked and worked well. It finally occurred to me that there was no way it was ever going to work as when the J Relay pulled in for a fraction of a second, the ball was kicked to the plunger and over the trough switch long after the J Relay had disengaged. That's when I realized something should be holding the J Relay on until SB2 is dropped out after the game starts. Not much in that circuit so I started looking at the reset switches and found a bad one on the 100s unit. That unit would actually reset fine but one of the two NO switches wasn't closing when at Zero. I guess one switch must be in the stepper circuit for the reels and the other for the 1st Ball Relay circuit. Adjusting that switch did the trick