Cremer (U-333) talks about the British sabotage propaganda effort (dropping leaflets and such). He says that "In the first years of the war it was highly improbably that German U-boat men were ready to sabotage their own boat. The British probably did not expect that they would, but counted rather on generating a certain mistrust, praticularly between the chief engineer and his mechanics. Whether the British ever succeeded, I cannot say."
So I guess you COULD be right in saying that it went on in the later years. I find it hard to believe, though. But what do I know.
