The reeds and reed plates of this Melodion were dirty and discolored. It was also seriously out of tune. Lowboy and I have both come to the conclusion that the typical vintage melodica (excepting some older models with wooden parts or crumbly gasket material) is significantly improved by a soak in a water-vinegar mix followed by thorough rinsing and drying. This almost always improves key action. I also clean the reeds carefully with a soft toothbrush and baking soda (or even toothpaste in problem cases). These preliminaries affect tuning and gapping.
This particular Melodion was wildly out of tune, and re-tuning was complicated by a previous owner’s having made crude tuning attempts in which some reeds were gouged. You may be able to see some gouging if you look carefully. All reeds are, however, fully functional. I re-tuned to A=440. It was necessary to widen the gaps of quite a few reeds, partly because of pre-existing problems, but also partly as result of my toothbrushing.
After cleaning. Some discoloration (and slight corrosion?) remains, since I didn’t want to get into scraping. But that could be done with the variable speed electric engraver, and I would do it except that in this case there was already so much tuning to do.