Yamaha CVP-300 panel

Hello! I‘ve been using my CVP-303 for many years and recently, a serious issue with the panel started. None of the panel buttons work anymore, only volume. This issue started with the panel working unreliably before completely losing its functionality. The display works normally.
I expect it to be a connection issue between panel and inner parts. Maybe a connecting cable which always is being bent when opening the piano lid has aged and now doesn‘t work anymore.

Do you have any ideas or suggestions?

Thank you very much in advance!