can you post a pic of the schem showing the game over relay circuit?
the schem I have (and I uploaded to ipdb) doesn't have a motor switch in the game over relay circuit. If the ball count unit is stepped up enough to turn on the game over light, there should be 24V when measuring on the terminals of the game over trip relay coil until the relay trips, at which time the hot side of the 24V is cut off to a bunch of stuff, including the game over trip coil.
continuity will tell you if there's an open circuit, but it won't tell you if a closed circuit is able to carry the required current. A voltmeter or a jumper wire will find poor connection issues that a continuity test won't.
how did you measure the resistance of the coil? Was a wire disconnected from the coil or did you ensure the ONLY path between the meter probes was thru the coil (lock relay switch open, ball count unit reset, no tilt switches closed).
a bad solder joint at the coil is a possibility. Depending on where the probes are touching, things may look ok with meters but you don't have a good circuit. The quick test is jumper from the yellow wire that's going all over the place (like lamps, flipper button switches, etc.) to the yellow-red wire on the game over trip coil and see if it trips.