I made these sashes and the box frames over 20 years ago, and they have
been very sadly neglected. Having purchased a nice selection of
Mighton's draughtproofing products, I have been removing the sashes to
apply them.

This is what the top meeting rail and bottom rail look like:

https://i.ibb.co/fx5HWqF/IMG-20210615-164657.jpg
https://i.ibb.co/jT4rzgT/IMG-20210615-164705.jpg
https://i.ibb.co/TkpTtgB/IMG-20210615-191213.jpg
https://i.ibb.co/kqsWRxT/IMG-20210615-191221.jpg
https://i.ibb.co/ZThN0bt/IMG-20210615-191235.jpg

On another window, I did a proper job and replaced the rotten rails, but
this one I'm hoping to bodge.

Am I expecting too much of wood hardener/filler?