I've seen a lot of people complaining that they can't view the availability of seats for games unless it's their turn to buy tickets, so I thought I'd post this work-around to help out. Mods, let me know if this should be elsewhere or isn't acceptable...
This will work for all browsers, but I use Chrome.
Go to the ticket section and right-click the greyed-out button, then click 'Inspect'.
Find the onclick event in the HTML and double click the URL that begins with 'en-GB'.
Copy and paste the URL to the end of https://tickets.lcfc.com/ like so
https://tickets.lcfc.com/en-GB/events/leicester city v liverpool (carabao cup)/2017-9-19_19.45/king power stadium?hallmap
and you're done.
Use the seat selection as you normally would, but obviously be aware it won't let you add tickets to your basket.
Hope this helps people buying tickets in the future.