Kingfisher,
As Pileatus suggested, but so briefly you may not have gotten his meaning, the thin straight line you are seeing is the roof edge of the Schmidt-Pechan prism. It is therefore not a crack, and probably not a problem either. Just about any roof-prism binocular will show it, especially if you view backwards through the binoculars towards a bright light source. It is a problem if it is not ground fine enough, when it can cause spiking in stars or bright light sources in normal viewing, and sometimes in cheap binoculars even a darker diagonal shadow line across the view when looking against a uniform background such as gray clouds or blue sky. In a Swarovski binocular, I have not yet seen a poor roof edge. The reason you could see it so well must have something to do with the condensation, as you said it disappeared mostly after the condensation vanished.
The condensation on the other hand is a clear flaw, and should not happen. What were the circumstances in which it happened? I suppose it must have leaked when you flushed the focusing mechanism, but a waterproof binocular must take a bit of tap water without a problem.
Kimmo