Stefan, the above is what I meant by "is using `read-key' inside of
`track-mouse' an acceptable stopgap solution?".

> Btw, it seems like "C-h k" is not really working for complex mouse
> clicks even without xterm-mouse-mode.  For example, try this:
>
>   C-h k C-mouse-3
>
> This pops up a menu; select any item from that menu.  The expected
> result is to get the description of the menu item you selected, but
> instead you get the prompt for "following key, mouse click, or menu
> item" anew.

This worked fine in Emacs 25.2, FWIW.