You will have to strip it down to inspect the cb board for any cracks.
If the cb board is ok you have a good chance of fixing this issue.
Try cleaning the cb contact areas with isopropyl alcohol 90%.
A good contact should have a reading of up to 300kohms.
after cleaning the contact areas,inspect the contact areas on the bottoms of the flex buttons.
Don't use isopropyl on the buttons,as the alcohol can dry the oils out and ruin the rubber.
Use silver contact paint on the bottoms of the flex buttons (paint each contact).This should restore the conductivity.
The silver conductive paint can be purchased from most electronic retailers,but I use the silver conductive paint for repairing continuity breakages on cars heated screens,(available from halfords).
Or you could buy a repair kit,.I have used these in the past for expensive keypad repair, and worth the money, even though some kits are only good for one application due to poor shelf life.
If you decide to attempt this repair,Ensure you isolate the power to the panel,and have the user manual at hand for reference.