Thanks! Yes: I was trying to hurry back here and post again to say that I have read all the Pro 36 posts and had seen your recommendation about the soapy water, so you wouldn’t have to repeat yourself again :-), but you beat me to it.
I’m going to see if I can come up with a smoke method just because it seems a little easier… hopefully there is a simple and non-harmful (to me or the instrument!) way to make enough visible smoke.
I had some leaks around the ends of the melodica where the metal plate blocks of the channel through the end blocks (old resin) which I sealed with accordion wax. And I replaced the main gasket with accordion bellows tape so I think it’s holding pretty well.