This is likely just 12 years' accumulated crud in the controls.
There are instructions on the board here for cleaning the "pots" with electronic cleaner spray. Takes longer to get the radio out than it does to do the cleaning. Odds are that it will cure your problem; gamble a couple bucks on the spray cleaner and about 30 minutes on the job.
remove radio
open up bottom of radio (tiny screws--keep track of them)
spray cleaner on the mechanism attached to the volume knob, rotate knob repeatedly along with moving it through range of motion for balance, etc.
reassemble and reinstall.
Radio Shack sells the cleaner in a small spray bottle for just a few bucks.
If you decide you just want to have a new head unit anyway, let me know what you want for the discarded CR 814.
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We have met the enemy and they is us. [Pogo] S70 T5 cop car : Rough Rider suspension, Walmart fog lights, eBay speakers, ambiance by Pall Mall, trim by Le Duc d'Tape, 8-channel THD by OEM amps