Personally I would keep the coin if you can confirm its a die crack opposed to a scratch. Whilst it may not affect the value, if there was any difference in price it would be a slight premium. Just for future notice, if you ever return a coin because you've found an error, the mint no longer provide you with a letter detailing the error and return it...they take the error in and give you a replacement. Definitely do not send in any nice errors else you will lose them