Primarily because of the age of the Sony product it's best to go directly to Sony Customer Service. It's highly unlikely that Best Buy will be able to assist you with a lifetime warranty because that warranty is between you and the company not you and the retailer.
@Michael is correct, especially since your radio is already 8 years old. Most likely they will no longer carry that model anymore, so they can't process the warranty for you. Although it probably won't hurt to back to best buy first and check with them. From my past experience with Sony customer service, I recommend just buying another radio if best buy can't help.
Contact sony best way to resolve it!!
The lifetime warranty wouldn't be through Best Buy. Call Sony customer service on that. They'll want the model# and maybe serial# if it has one.
Go back to best buy let them check it out
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