Maybe a service manual would do good, or maybe your friend that took the keys from the other KN could guide you how to replace?
The servicemanual would be good to have, but unfornately I dont have any.
Another long shot could be to ask Walt Tenay if he still have the servicemanual avalable?
http://www.synthzone.com/forum/ubbthreads.php/topics/395521/Service_Manual_for_SXKN2400_anBut, it's quite a long time since this post was published, and I have not seen any post by Walt for a very long time.
Last post was September 2015 as far as I have found out by a search:
http://www.synthzone.com/forum/ubbthreads.php/topics/408097/