Regarding the "clean before de-rusting" issue. Yes, that is recommended, to get the maximum life (usefulness) from a quantity of Evaporust. However, I've soaked some filthy steel parts for extended periods without noticeable deterioration to the parent metal. I don't think contamination from dried oil/grime caused the deterioration of the threads. I have no hypothesis (except defective parent material) to explain the deterioration pictured. It's a puzzlement to me.