How the everloving flick-flack do I fix THIS? DESPERATE HELP NEEDED

Hi! We recently helped some friend clear out their now-ex neighbors apartment and he gifted us a box full of decorative enamel angels, one of them being this little guy in the photo I've added below.

I've noticed not only a weird smell to him, but also a sort of badly decayed board and perhaps a speaker(??) falling out underneath his drum. After pouring some IPA on the corroded parts it suddenly startet making some sound, a pretty dead sound. I think this little dude is supposed to either drum or do any type of melody, but I don't know because, well, it's broken.

Does anyone have any idea how to fix this?? I desperately want to restore this lil guy, including whatever the !&&* the feature inside his drum is supposed to be. I've never fixed anythinf like this before. I have no idea what topic to shove this little guy into, especially since there's no “other devices” tab, but I really hope someone can help! Even tiny ideas on how to fix him are entirely acceptable!

More pictures of the board and the (perhaps) speaker below.

weird plastic piece, probably to hold this whole thing somehow together.