Hi George,
This older thread has some suggestions:
https://www.winnieowners.com/forums/...ng-350173.html
It might just be that you replace the radio and see if that fixes it. Because both speakers B and C are not working, it doesn't seem like it is a speaker problem, as that would indicate a double failure (or quadruple if counting individual speakers.)
Of course, the radio may have just become "unplugged" and that has caused the failure. It looks like you will need to pull the radio out and see what you can find.
Good luck; Eagle5