Xtol failures: there's been a lot of stuff written implicating iron, and perhaps other trace metals, in the water supply. This would not explain failures with (properly) distilled water. Kodak *might* have made some improvements to the formula but that is simply a *guess* of mine. I mix it double strength on the assumption that it will keep better, then dilute appropriately. I use it only occasionally, and I still get nervous, though I have never had a failure.