Another diagnostic idea. Is it practical to reverse the wiring between the transformer and track lock-on (xfmr red to lock-on black, and xfmr black to lock-on red so to speak)? Or perhaps just reverse connect to a short section of track and lock-on if more convenient?
If so, this would swap the Horn and Whistle button. The ability to blast short Horns, how long you must press Bell to turn it on/off, and general responsiveness should be the same as before except triggered with the opposite button.