I've edited my entire post #9 as Mr. Crossley has a better solution that
we can apply to our own servers by editing the .htaccess file. It will affect what everyone sees as your Banner and should not require any editing of the WC software. I would rather he post the <IfModule mod_expires.c> ... </IfModule> code since this file can affect your whole site. If you decide to make the change, be sure to make a copy of the original .htaccess file
BEFORE editing it.
uhmm... apparently, the last time I upgraded WC, I forgot to check the "FTP To Custom Web:" checkbox. Thus, the last update of my banner was that same date ~11 July 2018. It updates a lot faster now...