Fact, or Friction?
I will have to double check, but in my conversations with Seiseki Abe Shihan, I recall him mentioning this subject to me. I cannot say for sure if he said that O-Sensei himself had trained while in China. However, he did, and I mean definitely said that O-Sensei told Abe Sensei to go to China and study certain martial art related things there. Abe Sensei did in fact do this, and there are some remarkable stories he then related about his experiences there. I won't repeat them here, but I will commit to asking Abe Sensei about any specific details of O-Sensei's experiences that O-Sensei may have shared with him, when I next have the chance. I will report anything I may discover.
The only thing I would like to add is that I am sure that there are many things that O-Sensei may have shared with people that he did not share with his son. My father doesn't share plenty of things with me. I relate plenty of things about specific aikido students of mine to my friends that I never share with anyone in the dojo. I think it behooves us to remember that the master-student relationship that was in effect between O-Sensei and 99.9% of those around him inherently dictated what could and could not be shared.