I asked what crack was on the bike because we had a customer come in and have the same problem with his Dura-Ace crankset. The solution we came up with was replacing the chainrings with 105 model chainrings. Both the Dura-Ace and 105 are aluminum but the Dura-Ace are made from a lighter aluminum which makes them prone to premature wear. The 105 and Ultegra's are aluminum but since the aluminum composition is different it makes them slightly stronger but with a weight penalty.