I can see that there’s some unevenness in the spacing between keys. The white keys at the high end are tightly pressed together, and you can see some loose spacing in the rest of the keyboard, especially at the low C, which is elevated. With these old Italians this is pretty common. Lately with these old Italians, I do some work evening out the spacing of the whole keyboard. With any melodica, this problem at a particular place on the keyboard can be resolved without taking it apart. I used to insert a small knife blade between keys that are sticking or even just too close for comfort, and then push gently on one or both to open the tight gap, and more generally to close noticeably wide gaps. Eventually, it dawned on me that it’s easier to just depress the adjacent key and push the other key away with my finger. Pulsate a few times, and it won’t come all the way back. It’s pretty easy to to even out a whole keyboard in a few minutes. It may need to be revisited occasionally.
Look at the spacing on some of your other melodicas. If the keys are all working smoothly, uneven spacing doesn’t seem to affect performance, but it affects the visual aesthetics of the instrument. It can make a melodica look cheap and junky.
That low C could be fixed, I think, but it probably would require taking the Silvertone apart — though maybe you could figure out how to do it with just the end piece removed.