@GeoPeg and @texastrain
I made another attempt to get this working correctly based upon your suggestions, without much success.
1) Performed an air leak test with painters tape around the casing to cover seal. Also had a small section of tissue and checked for air movement around the gasket seal. There was no leakage seen with no improvement in the sound.
2) Inspected the gasket seating along the casing internals and outer edge. Here is a pic of the sealing outline. Looks like all the internal chambers are making contact.
3) The missing piece along the bottom edge is actually a smooth intentional section of the casting, from what I can see. This area is also sealed with the gasket.
4) Used a Starrett ruler and verified that the cover plate is flat. The top and bottom edges of the casting have depressions in them when the ruler is laid across the corner screw holes. Tried to place a strip of paper or thin cardboard to fill the gap. Neither attempt worked. When the center screw is tightened With just the gasket it pulled the cover in and seals so the upper whistle sounds.
Thanks for your interest and suggestions.
At this time its back on the layout for the grandkids to use with just the single tone. I guess I will be on the hunt for a donor tender.
