If DIY fails, try contacting Approved Audio in Bantam, CT. They were a CAL repair center and have an extensive inventory of parts. Fixed my CL-10 just fine. Maybe a little slow but know CAL gear in and out.
A lot of buttons are a contact with a carbon spot on a curcuit board behind the physical button plastic. (Like in remote controls.) it probably comes apart and need to be cleaned inside IMO. Otherwise a replacement button is in order.