T-Man,
Two thoughts ...
1. If I understand you, the aft-most "washer disc" (or valve, I guess) has been inadvertently pushed back too far, away from the edge of the big side opening window. But there's no easy way to grab it and move it back into position, with the resonator reed in the way. (Do I have that right?) If so, I'm wondering if the misplaced valve is magnetic? Can you poke in there with a strong (but small) magnet, grab it (magnetically), and wiggle it back into position? Or, if not that, maybe temporarilly super-glue a little grab stick to it's face, wiggle it into position, then break off the stick?
2. In your service info link, did you see the trick to add some diodes to the circuit to have the chugger stop chugging when the loco is kicked into neutral? Right up your alley.
Cheers,
TJ