The Ball Shooter coil requires a normally open switch to close on the O relay, a normally closed switch on the W relay, and a normally open switch at score motor 2C to close.

The same score motor 2C switch causes the credit unit to decrement at game start, so if that works, then that switch is working.

That would then narrow it to the switch on the O relay or the switch on the W relay. You said the Ball Return relay (which is O) is activating, so the switch there should be closing. But a wire could have popped off the switch tab (cold solder joint), or the switch isn't closing quite enough now. Or the switch on W may have had a wire pop off or the switch open slightly.

But O and W might be good places to inspect carefully.