I had many similar problems with my Kenwood remotes. Something seemed to always key spilled on them and provided invisible films to make the buttons not make contact. Washing the buttons with soap and water seems to work well. The circuit board also needs good cleaning, but with isopropyl alcohol or similar. Polishing contacts with pencil erasers also works in many cases. As a last resort, they do make bottles of refinishing material to recoat the button contacts.

Fred