If the short is really between those two points even with the rectifier completely out of the circuit, then it seems like more than just a component failure (since presumably nothing else in the schematics besides the rectifier connects them). Sounds like you have a short somewhere in the actual game wiring. It seems like you've been pretty systematic about isolating the failure down .. I don't have much advice except to keep going with that approach and you'll find it. Either isolate sections of the wiring, or you might get lucky just visually tracing that part of the wiring (the negative side of the DC doesn't really connect to that many places).

I love it when a plan comes together! It sounded like you were on the right track, and it was just a matter of time. For sure isolating it to the relatively small DC circuit was a huge clue.