You could, but honestly, the buyer is getting AppleCare with a used computer so he or she is protected until that expires. If the drive is running fine, than I say it's on the buyer to research any potential issues with the model they are puchasing.
Unless you're selling to a close friend or relative, not sure I would be doing a stranger I'll never see again that type of favor. Lugging a 27" iMac to an Apple Store is not fun. Trust me.