Are you comfortable working on the engine yourself?
The magnet ring is on the flywheel on the motor. It's part of the sensor system that allows Odyssey/Legacy, or whatever system your engine has to monitor the speed of the motor. Without being able to monitor the motor's actual speed, the system thinks it needs to go faster. That's why the loco takes off and rockets down the track.
The fix can be to:
-repair/replace the magnet ring somehow (if indeed it is bad),
-or position/realign the sensor that looks at the magnet ring (if it is out of position)
-or maybe some internal plugs need to be unplugged and plugged back in to eliminate micro corrosion.
-or maybe install a Cruise Commander M from electric railroad.
If you are not comfortable working on it, by all means DON'T. There is nothing quite like trying to fix something that someone else took apart, put back together wrong and now it is FUBAR.
