I came up with a fix for this problem. Once you get into the radio and get
the volume control switch out, you can carefully cut the melted plastic
rivits off, leaving enough to re-melt to close it back. There is a small
white nylon plastic slider inside the mechanism that is the problem. The
little pin on the side of the push rod slides in and out, selecting a
different channel each push, making it stay in or out, depending on which
little channel it goes in. Anyway, a tiny amount of white lithium grease
applied to that little nylon slider fixes it perfectly. That slider must
be free to move and when it gets just so dry, it refuses to move freely
anymore. The greast fixes the problem. With some care, you can
re-assemble the switch and remelt the plastic rivit pins to hold the
switch together. I did it and it works like new now. Sam.