Hi TJK,
I'm quoting
@jdurbin1 Here "The sticky goo is a doping compound that provides sealing, mass, and resonance control. It's a pita to live with but part of the magic sonically."
It can be repaired by Richard So here:
https://www.adsspeakersservice.com/
Aesthetically it may not look too appealing, but sonically, it may function properly and without any noticeable issues. Currently, Mr So does not have any inventory on new midrange domes, however he is able to clean them and inspect the driver for any issues it may have with voice coils and replace the sticky material. Hope that helps. Also pulling the midrange driver can be challenging, and recommend asking for help here if you cross that bridge. Don't pry the driver out, this could cause damage to the baffle.
Garry~