Likely it's a dirty volume control. Get some of this:
RadioShack® TV Tuner Cleaner
Model: 6404315-1 | Catalog #: 64-148 RadioShack® TV Tuner Cleaner - RadioShack.com
Or some other product made to clean electric volume controls. Works best if sprayed directly into the volume control. Note, some disassembly required.
Likely the right speaker will work after the fade is cleaned as well.