Low volume 30-1146

I would suggest replacing the speaker.

There are no replacement boards available from MTH parts for the electronic whistles. There is no easy repair of that board either. Conversely, speakers from this time era are KNOWN to fail from the magnet structure failing and often locking the voice coil of the speaker from moving- hence weak sound.

Guess I'm out of luck.  I'm deaf in one ear so what I thought was low whistle was the whistle from an old rail sounds car a couple feet away with sounds off but still emitted a faint sound.  I did have another speaker which works and soldered it in and held it to my ear.  When pushing whistle It produced a buzz.  Bad 25 year old board?