The reason you havent come across it is because most people with an eno check an maintain their chain alignment , tension , and check for cog wear as trialsboy mentioned its not the freewheel to blame. So I have no idea why you are selling it. Give your bike some more attention and love and it will respond. Mine has been fine but I still own a previous second hand one from someone who didnt maintain all of the aboev so it was oval.