I had two examples (Gold Rush) that had the same issue. I reported it to the IPDB back in '04.
"A game owner reported to us that he has two examples of this game and both left the factory with the wiring incorrect on the right playfield score reel as compared to the schematic. Two wires were crossed on this right reel which caused incorrect scoring on some score reel combinations. We do not know how many other games left the factory with this wiring error."
You should contact them